diff --git a/utility-db/src/main/java/com/dua3/utility/db/DbUtil.java b/utility-db/src/main/java/com/dua3/utility/db/DbUtil.java
index 5e9db532..0685127a 100644
--- a/utility-db/src/main/java/com/dua3/utility/db/DbUtil.java
+++ b/utility-db/src/main/java/com/dua3/utility/db/DbUtil.java
@@ -65,8 +65,9 @@ public final class DbUtil {
         try {
             // load properties
             Map<Object, Object> p;
-            try (InputStream in = DbUtil.class.getResourceAsStream("jdbc_drivers.properties")) {
-                p = LangUtil.loadProperties(in);
+            String resource = "jdbc_drivers.properties";
+            try (InputStream in = DbUtil.class.getResourceAsStream(resource)) {
+                p = LangUtil.loadProperties(Objects.requireNonNull(in, "resource nott found: " + resource));
             }
 
             // parse entries
@@ -287,8 +288,7 @@ public static DataSource createDataSource(Driver driver, String url, String user
             throws SQLException {
         LangUtil.check(driver.acceptsURL(url), () -> new SQLException("URL not accepted by driver"));
 
-        JdbcDataSource ds = new JdbcDataSource();
-        ds.setDriver(driver);
+        JdbcDataSource ds = new JdbcDataSource(driver);
         ds.setUrl(url);
         ds.setUser(user);
         ds.setPassword(password);
diff --git a/utility-db/src/main/java/com/dua3/utility/db/JdbcDataSource.java b/utility-db/src/main/java/com/dua3/utility/db/JdbcDataSource.java
index d5aeb02c..e4304bfd 100644
--- a/utility-db/src/main/java/com/dua3/utility/db/JdbcDataSource.java
+++ b/utility-db/src/main/java/com/dua3/utility/db/JdbcDataSource.java
@@ -28,13 +28,15 @@ public class JdbcDataSource implements DataSource {
     private @Nullable String url;
     private @Nullable PrintWriter logWriter;
     private int loginTimeout;
-    private @Nullable Driver driver;
+    private Driver driver;
 
     /**
      * Constructor.
+     *
+     * @param driver the driver
      */
-    public JdbcDataSource() {
-        // nop
+    public JdbcDataSource(Driver driver) {
+        this.driver = driver;
     }
 
     private void log(String message) {
@@ -43,15 +45,6 @@ private void log(String message) {
         }
     }
 
-    /**
-     * Set the JDBC driver for this instance.
-     *
-     * @param driver the driver
-     */
-    public void setDriver(Driver driver) {
-        this.driver = driver;
-    }
-
     @Override
     public Logger getParentLogger() throws SQLFeatureNotSupportedException {
         throw new SQLFeatureNotSupportedException("getParentLogger() is not supported");
diff --git a/utility-db/src/main/java/com/dua3/utility/db/NamedParameterStatement.java b/utility-db/src/main/java/com/dua3/utility/db/NamedParameterStatement.java
index fcd20a33..82373c88 100644
--- a/utility-db/src/main/java/com/dua3/utility/db/NamedParameterStatement.java
+++ b/utility-db/src/main/java/com/dua3/utility/db/NamedParameterStatement.java
@@ -121,7 +121,7 @@ public NamedParameterStatement(Connection connection, String query) throws SQLEx
         statement = connection.prepareStatement(parsedQuery);
     }
 
-    private static JDBCType getParameterType(ParameterMetaData meta, int index) {
+    private static @Nullable JDBCType getParameterType(ParameterMetaData meta, int index) {
         try {
             return JDBCType.valueOf(meta.getParameterType(index));
         } catch (SQLException e) {
@@ -281,7 +281,7 @@ private <T> void setNonNullWithLongArg(String name, T value, long arg, SetParame
         }
     }
 
-    private <T, U> void setWithObjectArg(SQLType type, String name, @Nullable T value, @Nullable U arg, SetParameterObject<T, U> setter) throws SQLException {
+    private <T, U> void setWithObjectArg(SQLType type, String name, @Nullable T value, @Nullable U arg, SetParameterObject<T, @Nullable U> setter) throws SQLException {
         if (value == null) {
             setNull(name, type);
         } else {
@@ -1152,7 +1152,7 @@ private interface SetParameterObject<T, U> {
     public static class ParameterInfo {
         final String name;
         final List<Integer> indexes = new ArrayList<>();
-        JDBCType type;
+        @Nullable JDBCType type;
 
         ParameterInfo(String name) {
             this.name = name;
diff --git a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/AbstractDialogBuilder.java b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/AbstractDialogBuilder.java
index 03b193cf..94d0439d 100644
--- a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/AbstractDialogBuilder.java
+++ b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/AbstractDialogBuilder.java
@@ -34,7 +34,7 @@ public abstract class AbstractDialogBuilder<D extends @NonNull Dialog<R>, B exte
         extends AbstractDialogPaneBuilder<D, B, R> {
 
     private final BiConsumer<D, String> titleSetter;
-    private @Nullable final Window parentWindow;
+    private final @Nullable Window parentWindow;
     private @Nullable String title;
 
     protected AbstractDialogBuilder(@Nullable Window parentWindow) {
diff --git a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/AlertBuilder.java b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/AlertBuilder.java
index fbc4c647..a6dcd790 100644
--- a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/AlertBuilder.java
+++ b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/AlertBuilder.java
@@ -36,7 +36,7 @@ public class AlertBuilder
     private ButtonType @Nullable[] buttons;
     private @Nullable ButtonType defaultButton;
 
-    AlertBuilder(AlertType type, Window parentWindow) {
+    AlertBuilder(AlertType type, @Nullable Window parentWindow) {
         super(parentWindow);
         setDialogSupplier(() -> new Alert(type));
     }
diff --git a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/ChoiceInputControl.java b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/ChoiceInputControl.java
index 0d7f9d2f..169ef6eb 100644
--- a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/ChoiceInputControl.java
+++ b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/ChoiceInputControl.java
@@ -9,6 +9,7 @@
 import javafx.beans.property.SimpleStringProperty;
 import javafx.scene.Node;
 import javafx.scene.control.ComboBox;
+import org.jspecify.annotations.Nullable;
 
 import java.util.function.Supplier;
 
@@ -17,7 +18,7 @@
  *
  * @param <T> the input result type
  */
-public class ChoiceInputControl<T> implements InputControl<T> {
+public class ChoiceInputControl<T extends @Nullable Object> implements InputControl<T> {
 
     private final ComboBox<ChoiceOption.Choice<T>> control;
     private final ChoiceOption<T> option;
diff --git a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/ComboBoxEx.java b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/ComboBoxEx.java
index 0790e573..28768b05 100644
--- a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/ComboBoxEx.java
+++ b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/ComboBoxEx.java
@@ -1,5 +1,7 @@
 package com.dua3.utility.fx.controls;
 
+import javafx.beans.property.SimpleBooleanProperty;
+import javafx.beans.property.SimpleStringProperty;
 import org.jspecify.annotations.Nullable;
 import javafx.beans.binding.Bindings;
 import javafx.beans.property.Property;
@@ -36,7 +38,7 @@
  *
  * @param <T> the type of the items contained in the ComboBox
  */
-public class ComboBoxEx<T> extends CustomControl<HBox> implements InputControl<T> {
+public class ComboBoxEx<T extends @Nullable Object> extends CustomControl<HBox> implements InputControl<T> {
     private static final Logger LOG = LogManager.getLogger(ComboBoxEx.class);
 
     private @Nullable Comparator<? super T> comparator = null;
@@ -143,6 +145,11 @@ protected void updateItem(@Nullable T item, boolean empty) {
     }
 
     private void editItem() {
+        if (edit == null) {
+            LOG.warn("editing not supported");
+            return;
+        }
+
         int idx = comboBox.getSelectionModel().getSelectedIndex();
         if (idx >= 0) {
             T item = items.get(idx);
@@ -157,7 +164,7 @@ private void editItem() {
     }
 
     private void addItem() {
-        Optional.ofNullable(add.get()).ifPresent(item -> {
+        Optional.ofNullable(add).map(Supplier::get).ifPresent(item -> {
             items.add(item);
             comboBox.getSelectionModel().select(item);
             sortItems();
@@ -280,11 +287,11 @@ public void reset() {
 
     @Override
     public ReadOnlyBooleanProperty validProperty() {
-        return null; // FIXME
+        return new SimpleBooleanProperty(true);
     }
 
     @Override
     public ReadOnlyStringProperty errorProperty() {
-        return null; // FIXME
+        return new SimpleStringProperty("");
     }
 }
diff --git a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/FileChooserBuilder.java b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/FileChooserBuilder.java
index de205d1a..b5452c01 100644
--- a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/FileChooserBuilder.java
+++ b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/FileChooserBuilder.java
@@ -43,7 +43,7 @@ public class FileChooserBuilder {
     private Path initialDir = USER_HOME;
     private String initialFileName = "";
     private List<ExtensionFilter> filters = new ArrayList<>();
-    private ExtensionFilter selectedFilter = null;
+    private @Nullable ExtensionFilter selectedFilter = null;
 
     FileChooserBuilder() {
     }
diff --git a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/FileInput.java b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/FileInput.java
index 969591d6..11bce8f9 100644
--- a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/FileInput.java
+++ b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/FileInput.java
@@ -44,7 +44,7 @@
  * These properties are updated based on the path selected by the user and the
  * specified validation function.</p>
  */
-public class FileInput extends CustomControl<HBox> implements InputControl<Path> {
+public class FileInput extends CustomControl<HBox> implements InputControl<@Nullable Path> {
 
     private static final StringConverter<Path> PATH_CONVERTER = new PathConverter();
 
@@ -60,11 +60,11 @@ public Path fromString(@Nullable String s) {
         }
     }
 
-    private final ObjectProperty<Path> value = new SimpleObjectProperty<>();
+    private final ObjectProperty<@Nullable Path> value = new SimpleObjectProperty<>();
 
     private final FileDialogMode mode;
     private final FileChooser.ExtensionFilter[] filters;
-    private final Supplier<Path> dflt;
+    private final Supplier<@Nullable Path> dflt;
 
     private final StringProperty error = new SimpleStringProperty("");
     private final BooleanProperty valid = new SimpleBooleanProperty(true);
@@ -83,7 +83,7 @@ public FileInput(
             boolean existingOnly,
             Supplier<Path> dflt,
             Collection<FileChooser.ExtensionFilter> filters,
-            Function<Path, Optional<String>> validate) {
+            Function<@Nullable Path, Optional<String>> validate) {
         super(new HBox());
 
         getStyleClass().setAll("file-input");
@@ -208,7 +208,7 @@ public static Function<Path, Optional<String>> defaultValidate(FileDialogMode mo
         };
     }
 
-    private Path getPath() {
+    private @Nullable Path getPath() {
         return value.get();
     }
 
@@ -223,7 +223,7 @@ public void reset() {
     }
 
     @Override
-    public Property<Path> valueProperty() {
+    public Property<@Nullable Path> valueProperty() {
         return value;
     }
 
diff --git a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/InputBuilder.java b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/InputBuilder.java
index 8fa8e36a..94c56691 100644
--- a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/InputBuilder.java
+++ b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/InputBuilder.java
@@ -286,7 +286,7 @@ default <T> B comboBoxEx(
             @Nullable Supplier<T> add,
             @Nullable BiPredicate<ComboBoxEx<T>, T> remove,
             Function<T, String> format,
-            Supplier<T> dflt,
+            Supplier<@Nullable T> dflt,
             Class<T> cls,
             Collection<T> items
     ) {
@@ -333,7 +333,7 @@ <T> B comboBoxEx(
      * @param items the items to choose from
      * @return {@code this}
      */
-    default <T> B radioList(
+    default <T extends @Nullable Object> B radioList(
             String id,
             String label,
             Supplier<T> dflt,
diff --git a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/InputGrid.java b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/InputGrid.java
index 152dca7a..7c748a1b 100644
--- a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/InputGrid.java
+++ b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/InputGrid.java
@@ -17,6 +17,7 @@
 
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -41,7 +42,7 @@ public class InputGrid extends GridPane {
     private static final String MARKER_OK = "";
 
     protected final BooleanProperty valid = new SimpleBooleanProperty(false);
-    private Collection<Meta<?>> data = null;
+    private Collection<Meta<?>> data = Collections.emptyList();
     private int columns = 1;
 
     /**
@@ -166,12 +167,12 @@ public void reset() {
      *
      * @param <T> the input's value type
      */
-    static final class Meta<T> {
+    static final class Meta<T extends @Nullable Object> {
         final String id;
         final Class<T> cls;
         final Supplier<? extends T> dflt;
         final InputControl<? super T> control;
-        final Label label;
+        final @Nullable Label label;
         final Label marker = new Label();
 
         Meta(String id, @Nullable String label, Class<T> cls, Supplier<? extends T> dflt, InputControl<? super T> control) {
diff --git a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/InputGridBuilder.java b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/InputGridBuilder.java
index fd12afa3..e9c5b54c 100644
--- a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/InputGridBuilder.java
+++ b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/InputGridBuilder.java
@@ -74,7 +74,7 @@ static class ControlWrapper implements InputControl<Void> {
 
         private final Node node;
 
-        private final Property<Void> value = new SimpleObjectProperty<>(null);
+        private final Property<Void> value = new SimpleObjectProperty<>();
         private final BooleanProperty valid = new SimpleBooleanProperty(true);
         private final ReadOnlyStringProperty error = new SimpleStringProperty("");
 
@@ -120,7 +120,7 @@ private <T> InputGridBuilder doAdd(String id, @Nullable String label, Class<T> t
 
     @Override
     public InputGridBuilder addNode(String id, @Nullable String label, Node node) {
-        Meta<Void> meta = new Meta<>(id, label, Void.class, null, new ControlWrapper(node));
+        Meta<Void> meta = new Meta<>(id, label, Void.class, () -> null, new ControlWrapper(node));
         Meta<?> prev = data.put(id, meta);
         LangUtil.check(prev == null, "Input with id '" + id + "' already defined");
         return this;
@@ -128,7 +128,7 @@ public InputGridBuilder addNode(String id, @Nullable String label, Node node) {
 
     @Override
     public InputGridBuilder addNode(String id, Node node) {
-        Meta<Void> meta = new Meta<>(id, null, Void.class, null, new ControlWrapper(node));
+        Meta<Void> meta = new Meta<>(id, null, Void.class, () -> null, new ControlWrapper(node));
         Meta<?> prev = data.put(id, meta);
         LangUtil.check(prev == null, "Input with id '" + id + "' already defined");
         return this;
diff --git a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/OptionsPane.java b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/OptionsPane.java
index 556b779b..246a8da0 100644
--- a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/OptionsPane.java
+++ b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/OptionsPane.java
@@ -43,9 +43,9 @@ public class OptionsPane extends GridPane implements InputControl<Arguments> {
      */
     protected static final Logger LOG = LogManager.getLogger(OptionsPane.class);
     private static final Insets INSETS = new Insets(2);
-    private final InputControl.State<Arguments> state;
+    private final InputControl.State<@Nullable Arguments> state;
     private final Supplier<? extends Collection<Option<?>>> options;
-    private final Supplier<Arguments> dflt;
+    private final Supplier<@Nullable Arguments> dflt;
     private final Map<Option<?>, InputControl<?>> items = new LinkedHashMap<>();
 
     /**
@@ -71,7 +71,7 @@ public OptionsPane(Collection<Option<?>> optionSet, Arguments currentValues) {
     public OptionsPane(Supplier<? extends Collection<Option<?>>> options, Supplier<Arguments> dflt) {
         this.options = options;
         this.dflt = dflt;
-        Property<Arguments> value = new SimpleObjectProperty<>();
+        Property<@Nullable Arguments> value = new SimpleObjectProperty<>();
         this.state = new State<>(value, dflt);
     }
 
@@ -130,7 +130,7 @@ public void init() {
     }
 
     @SuppressWarnings("unchecked")
-    private <T> InputControl<T> createControl(Arguments values, Option<T> option) {
+    private <T extends @Nullable Object> InputControl<T> createControl(Arguments values, Option<T> option) {
         if (option instanceof ChoiceOption<T> co) {
             return new ChoiceInputControl<>(co, supplyDefault(co, values));
         } else if (option instanceof Flag f) {
@@ -189,7 +189,7 @@ public void reset() {
     }
 
     @Override
-    public Property<Arguments> valueProperty() {
+    public Property<@Nullable Arguments> valueProperty() {
         return state.valueProperty();
     }
 
diff --git a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/RadioPane.java b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/RadioPane.java
index 44ba9dab..1976ec58 100644
--- a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/RadioPane.java
+++ b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/RadioPane.java
@@ -28,7 +28,7 @@
  *
  * @param <T> The type of items that will be represented as radio buttons.
  */
-public class RadioPane<T> extends VBox implements InputControl<T> {
+public class RadioPane<T extends @Nullable Object> extends VBox implements InputControl<T> {
 
     protected static final Logger LOG = LogManager.getLogger(RadioPane.class);
     private static final double SPACING = 4;
@@ -58,7 +58,7 @@ public RadioPane(Collection<T> items, @Nullable T currentValue, Function<T, Opti
         }
 
         // update state when selected toggle changes
-        Property<T> property = new SimpleObjectProperty<>();
+        Property<@Nullable T> property = new SimpleObjectProperty<>();
         group.selectedToggleProperty().addListener((v, o, n) -> {
             Toggle toggle = group.getSelectedToggle();
             property.setValue(toggle != null ? (T) toggle.getUserData() : null);
diff --git a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/SimpleInputControl.java b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/SimpleInputControl.java
index e7512f69..8dfdebb5 100644
--- a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/SimpleInputControl.java
+++ b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/SimpleInputControl.java
@@ -5,6 +5,7 @@
 import javafx.beans.property.ReadOnlyStringProperty;
 import javafx.scene.control.Control;
 import org.jspecify.annotations.NonNull;
+import org.jspecify.annotations.Nullable;
 
 import java.util.Optional;
 import java.util.function.Function;
@@ -17,7 +18,7 @@
  * @param <C> the type of the control, which must extend from Control
  * @param <R> the type of the value held by the input control
  */
-public class SimpleInputControl<C extends @NonNull Control, R> implements InputControl<R> {
+public class SimpleInputControl<C extends Control, R extends @Nullable Object> implements InputControl<R> {
 
     private final C control;
     private final State<R> state;
diff --git a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/SliderBuilder.java b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/SliderBuilder.java
index b7589419..0d9169ca 100644
--- a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/SliderBuilder.java
+++ b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/SliderBuilder.java
@@ -4,6 +4,7 @@
 import javafx.beans.value.ObservableNumberValue;
 import javafx.geometry.Orientation;
 import javafx.scene.Node;
+import org.jspecify.annotations.Nullable;
 
 import java.util.function.BiFunction;
 import java.util.function.DoubleConsumer;
@@ -168,7 +169,7 @@ public SliderBuilder bind(ObservableNumberValue value) {
      * @param value the property to be bound bidirectionally with the slider's value property.
      * @return this instance of {@code SliderBuilder} for method chaining.
      */
-    public SliderBuilder bindBidirectional(Property<Number> value) {
+    public SliderBuilder bindBidirectional(Property<@Nullable Number> value) {
         slider.valueProperty().bindBidirectional(value);
         return this;
     }
diff --git a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/TableCellAutoCommit.java b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/TableCellAutoCommit.java
index 22df2feb..d60fba34 100644
--- a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/TableCellAutoCommit.java
+++ b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/TableCellAutoCommit.java
@@ -134,13 +134,14 @@ public void commitEdit(@Nullable T newValue) {
             TableView<S> table = getTableView();
             if (table != null) {
                 TableColumn<S, T> column = getTableColumn();
-                CellEditEvent<S, T> event = new CellEditEvent<>(
+                @SuppressWarnings("DataFlowIssue") CellEditEvent<S, T> event = new CellEditEvent<>(
                         table, new TablePosition<>(table, getIndex(), column), TableColumn.editCommitEvent(), newValue
                 );
                 Event.fireEvent(column, event);
                 Platform.runLater(table::refresh);
             }
         }
+        //noinspection DataFlowIssue
         super.commitEdit(newValue);
         setContentDisplay(ContentDisplay.TEXT_ONLY);
     }
diff --git a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/TextFieldBuilder.java b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/TextFieldBuilder.java
index 3340083d..14e3aeba 100644
--- a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/TextFieldBuilder.java
+++ b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/TextFieldBuilder.java
@@ -19,14 +19,16 @@
 public final class TextFieldBuilder {
 
     private static final Pattern INTEGER_PATTERN = Pattern.compile("\\d*|0");
-    private static final UnaryOperator<TextFormatter.Change> INTEGER_FILTER = change -> INTEGER_PATTERN.matcher(change.getControlNewText()).matches() ? change : null;
+    @SuppressWarnings("DataFlowIssue") // should be Function<Change, @Nullable Change> but type is incompatible
+    private static final UnaryOperator<TextFormatter.@Nullable Change> INTEGER_FILTER = change -> INTEGER_PATTERN.matcher(change.getControlNewText()).matches() ? change : null;
 
     private static TextFormatter<Integer> getIntegerTextFormatter(UnaryOperator<TextFormatter.Change> integerFilter) {
         return new TextFormatter<>(new IntegerStringConverter(), 0, integerFilter);
     }
 
     private static final Pattern SIGNED_INTEGER_PATTERN = Pattern.compile("-?([1-9]\\d*|0)?");
-    private static final UnaryOperator<TextFormatter.Change> SIGNED_INTEGER_FILTER = change -> SIGNED_INTEGER_PATTERN.matcher(change.getControlNewText()).matches() ? change : null;
+    @SuppressWarnings("DataFlowIssue") // should be Function<Change, @Nullable Change> but type is incompatible
+    private static final UnaryOperator<TextFormatter.@Nullable Change> SIGNED_INTEGER_FILTER = change -> SIGNED_INTEGER_PATTERN.matcher(change.getControlNewText()).matches() ? change : null;
 
     private @Nullable String text;
     private TextFieldType type = TextFieldType.TEXT;
diff --git a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/Validator.java b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/Validator.java
index 69a72531..69c63788 100644
--- a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/Validator.java
+++ b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/Validator.java
@@ -58,7 +58,7 @@
 public class Validator {
     private static final Logger LOG = LogManager.getLogger(Validator.class);
 
-    private final ResourceBundle resources;
+    private final @Nullable  ResourceBundle resources;
     private final LinkedHashMap<Control, List<Supplier<ValidationResult>>> controls = new LinkedHashMap<>();
     private final MapProperty<Control, ValidationResult> validationResultProperty = new SimpleMapProperty<>();
     private final BooleanProperty validProperty = new SimpleBooleanProperty();
diff --git a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/WizardDialog.java b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/WizardDialog.java
index 47c8ca05..6ec3d9ff 100644
--- a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/WizardDialog.java
+++ b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/WizardDialog.java
@@ -18,6 +18,8 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.Objects;
+import java.util.Optional;
 import java.util.Set;
 import java.util.function.Consumer;
 
@@ -106,6 +108,10 @@ public void setPages(Map<String, Page<?, ?>> pages, String startPage) {
      * @throws IllegalStateException if any page refers to a 'next' page that does not exist
      */
     private void checkPages() {
+        if (pages == null) {
+            return;
+        }
+
         Set<String> pageNames = pages.keySet();
         for (Entry<String, Page<?, ?>> entry : pages.entrySet()) {
             String name = entry.getKey();
@@ -153,7 +159,7 @@ private void checkPages() {
     }
 
     private void setPage(String pageName) {
-        this.current = Pair.of(pageName, pages.get(pageName));
+        this.current = Pair.of(pageName, Objects.requireNonNull(pages, "pages not set").get(pageName));
 
         InputDialogPane<?> pane = current.second().pane;
         setDialogPane(pane);
@@ -217,8 +223,8 @@ public boolean isShowPreviousButton() {
      *
      * @return the current wizard page as a {@link Page} object
      */
-    public Page<?, ?> getCurrentPage() {
-        return current.second();
+    public Optional<Page<?, ?>> getCurrentPage() {
+        return Optional.ofNullable(current).map(Pair::second);
     }
 
     /**
diff --git a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/WizardDialogBuilder.java b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/WizardDialogBuilder.java
index aa5d5785..954c6535 100644
--- a/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/WizardDialogBuilder.java
+++ b/utility-fx-controls/src/main/java/com/dua3/utility/fx/controls/WizardDialogBuilder.java
@@ -1,5 +1,7 @@
 package com.dua3.utility.fx.controls;
 
+import org.jspecify.annotations.Nullable;
+
 import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.Optional;
@@ -13,7 +15,7 @@ public class WizardDialogBuilder {
 
     final LinkedHashMap<String, WizardDialog.Page<?, ?>> pages = new LinkedHashMap<>();
     private String title = "";
-    private String startPage = null;
+    private String startPage = "";
 
     WizardDialogBuilder() {}
 
@@ -45,7 +47,7 @@ public <D extends InputDialogPane<R>, B extends AbstractPaneBuilder<D, B, R>, R>
         page.setNext(builder.next);
         pages.put(name, page);
 
-        if (startPage == null) {
+        if (startPage.isEmpty()) {
             setStartPage(name);
         }
 
diff --git a/utility-fx-db/src/main/java/com/dua3/utility/fx/db/FxDbUtil.java b/utility-fx-db/src/main/java/com/dua3/utility/fx/db/FxDbUtil.java
index 8f7de1b9..7b0a1e4a 100644
--- a/utility-fx-db/src/main/java/com/dua3/utility/fx/db/FxDbUtil.java
+++ b/utility-fx-db/src/main/java/com/dua3/utility/fx/db/FxDbUtil.java
@@ -28,6 +28,8 @@
 import javafx.util.Callback;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
+import org.jspecify.annotations.NonNull;
+import org.jspecify.annotations.Nullable;
 
 import java.sql.Clob;
 import java.sql.JDBCType;
@@ -95,11 +97,14 @@ public static int fill(TableView<ObservableList<Object>> tv, ResultSet rs) throw
             int scale = meta.getScale(i);
 
             // define the formatting
-            Function<Object, String> format;
+            Function<@NonNull Object, @NonNull String> format;
             switch (sqlType) {
-                case DATE -> format = item -> DbUtil.toLocalDate(item).format(dateFormatter);
-                case TIMESTAMP -> format = item -> DbUtil.toLocalDateTime(item).format(timestampFormatter);
-                case TIME -> format = item -> DbUtil.toLocalDateTime(item).format(timeFormatter);
+                case DATE -> //noinspection DataFlowIssue - format is not called for null arguments
+                        format = item -> DbUtil.toLocalDate(item).format(dateFormatter);
+                case TIMESTAMP -> //noinspection DataFlowIssue - format is not called for null arguments
+                        format = item -> DbUtil.toLocalDateTime(item).format(timestampFormatter);
+                case TIME ->  //noinspection DataFlowIssue - format is not called for null arguments
+                        format = item -> DbUtil.toLocalDateTime(item).format(timeFormatter);
 
                 // numbers that have scale
                 case DECIMAL, NUMERIC -> {
@@ -121,7 +126,7 @@ public static int fill(TableView<ObservableList<Object>> tv, ResultSet rs) throw
             LOG.trace("column name: {} label: {} type: {} scale: {}", name, label, sqlType, scale);
 
             // CellValueFactory
-            Callback<CellDataFeatures<ObservableList<Object>, Object>, ObservableValue<Object>> cellValueFactory
+            Callback<CellDataFeatures<ObservableList<Object>, Object>, ObservableValue<@Nullable Object>> cellValueFactory
                     = param -> {
                 var list = param.getValue();
                 var x = idx < list.size() ? list.get(idx) : null;
diff --git a/utility-fx-icons-ikonli/src/main/java/com/dua3/utility/fx/icons/ikonli/IkonliIconProvider.java b/utility-fx-icons-ikonli/src/main/java/com/dua3/utility/fx/icons/ikonli/IkonliIconProvider.java
index 1fc19805..e6754e9d 100644
--- a/utility-fx-icons-ikonli/src/main/java/com/dua3/utility/fx/icons/ikonli/IkonliIconProvider.java
+++ b/utility-fx-icons-ikonli/src/main/java/com/dua3/utility/fx/icons/ikonli/IkonliIconProvider.java
@@ -2,13 +2,16 @@
 
 import com.dua3.utility.fx.icons.Icon;
 import com.dua3.utility.fx.icons.IconProvider;
+import javafx.beans.property.IntegerProperty;
 import javafx.scene.Node;
+import javafx.scene.paint.Paint;
 import org.kordamp.ikonli.Ikon;
 import org.kordamp.ikonli.IkonHandler;
 import org.kordamp.ikonli.javafx.FontIcon;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 
+import java.util.Optional;
 import java.util.ServiceLoader;
 
 
@@ -31,19 +34,20 @@ public String name() {
     }
 
     @Override
-    public Icon forName(String name) {
+    public Optional<Icon> forName(String name) {
         for (var handler : ServiceLoader.load(IkonHandler.class)) {
             if (handler.supports(name)) {
                 LOG.debug("using: {}", handler.getClass().getName());
                 var ikon = handler.resolve(name);
-                return new IkonliIcon(ikon, name);
+                return Optional.of(new IkonliIcon(ikon, name));
             }
         }
 
         LOG.debug("icon not found: {}", name);
-        return null;
+        return Optional.empty();
     }
 
+    @SuppressWarnings("NullableProblems")
     static class IkonliIcon extends FontIcon implements Icon {
         private final String name;
 
@@ -52,6 +56,20 @@ static class IkonliIcon extends FontIcon implements Icon {
             this.name = name;
         }
 
+        @Override
+        public IntegerProperty iconSizeProperty() {
+            IntegerProperty p = super.iconSizeProperty();
+            assert p != null;
+            return p;
+        }
+
+        @Override
+        public Paint getIconColor() {
+            Paint c = super.getIconColor();
+            assert c != null;
+            return c;
+        }
+
         @Override
         public String getIconIdentifier() {
             return name;
diff --git a/utility-fx-icons/src/main/java/com/dua3/utility/fx/icons/IconProvider.java b/utility-fx-icons/src/main/java/com/dua3/utility/fx/icons/IconProvider.java
index 35f18a5d..8eb23519 100644
--- a/utility-fx-icons/src/main/java/com/dua3/utility/fx/icons/IconProvider.java
+++ b/utility-fx-icons/src/main/java/com/dua3/utility/fx/icons/IconProvider.java
@@ -1,5 +1,7 @@
 package com.dua3.utility.fx.icons;
 
+import java.util.Optional;
+
 /**
  * The IconProvider interface represents a provider of icons.
  */
@@ -15,7 +17,7 @@ public interface IconProvider {
      * Get icon.
      *
      * @param name name of the requested icon
-     * @return icon or {@code null} if this provider does not offer the requested icon
+     * @return Optional holding the icon
      */
-    Icon forName(String name);
+    Optional<Icon> forName(String name);
 }
diff --git a/utility-fx-icons/src/main/java/com/dua3/utility/fx/icons/IconUtil.java b/utility-fx-icons/src/main/java/com/dua3/utility/fx/icons/IconUtil.java
index c416a96e..38986699 100644
--- a/utility-fx-icons/src/main/java/com/dua3/utility/fx/icons/IconUtil.java
+++ b/utility-fx-icons/src/main/java/com/dua3/utility/fx/icons/IconUtil.java
@@ -37,7 +37,7 @@ public static Optional<Icon> iconFromName(String name) {
         return ServiceLoader.load(iconProviderClass)
                 .stream()
                 .peek(provider -> LOG.debug("found {} implementation: {}", iconProviderClass.getName(), provider.getClass().getName()))
-                .map(provider -> provider.get().forName(name))
+                .map(provider -> provider.get().forName(name).orElse(null))
                 .filter(Objects::nonNull)
                 .findFirst();
     }
diff --git a/utility-fx/src/main/java/com/dua3/utility/fx/FxLogPane.java b/utility-fx/src/main/java/com/dua3/utility/fx/FxLogPane.java
index 316035ee..2954c0e2 100644
--- a/utility-fx/src/main/java/com/dua3/utility/fx/FxLogPane.java
+++ b/utility-fx/src/main/java/com/dua3/utility/fx/FxLogPane.java
@@ -58,7 +58,7 @@ public class FxLogPane extends BorderPane {
     private final TextArea details;
     private final TableView<LogEntry> tableView;
 
-    private @Nullable volatile LogEntry selectedItem;
+    private volatile @Nullable LogEntry selectedItem;
 
     private boolean autoScroll = true;
 
diff --git a/utility-fx/src/main/java/com/dua3/utility/fx/FxRefresh.java b/utility-fx/src/main/java/com/dua3/utility/fx/FxRefresh.java
index 20e37fb2..c919ec02 100644
--- a/utility-fx/src/main/java/com/dua3/utility/fx/FxRefresh.java
+++ b/utility-fx/src/main/java/com/dua3/utility/fx/FxRefresh.java
@@ -60,10 +60,12 @@ public final class FxRefresh {
     private FxRefresh(String name, Runnable task) {
         this.name = name;
         this.task = task;
-        this.updateThread = new Thread(this::refreshLoop);
 
-        updateThread.setDaemon(true);
-        updateThread.start();
+        Thread thread = new Thread(this::refreshLoop);
+        thread.setDaemon(true);
+        this.updateThread = thread;
+
+        thread.start();
     }
 
     /**
diff --git a/utility-fx/src/main/java/com/dua3/utility/fx/FxUtil.java b/utility-fx/src/main/java/com/dua3/utility/fx/FxUtil.java
index 9ec68613..ae8076a2 100644
--- a/utility-fx/src/main/java/com/dua3/utility/fx/FxUtil.java
+++ b/utility-fx/src/main/java/com/dua3/utility/fx/FxUtil.java
@@ -523,7 +523,7 @@ public void accept(@Nullable T t1, @Nullable T t2) {
      * @param <T> the type of the value stored in the Value object
      * @return an ObservableValue object that reflects changes in the Value object
      */
-    public static <T> ObservableValue<T> toObservableValue(Value<T> value) {
+    public static <T extends @Nullable Object> ObservableValue<T> toObservableValue(Value<T> value) {
         return new ObservableValue<>() {
             @Override
             public void addListener(ChangeListener<? super T> listener) {
diff --git a/utility-fx/src/main/java/com/dua3/utility/fx/PlatformHelper.java b/utility-fx/src/main/java/com/dua3/utility/fx/PlatformHelper.java
index 72b62726..220d5b33 100644
--- a/utility-fx/src/main/java/com/dua3/utility/fx/PlatformHelper.java
+++ b/utility-fx/src/main/java/com/dua3/utility/fx/PlatformHelper.java
@@ -38,6 +38,7 @@ private PlatformHelper() {
     public static void runAndWait(Runnable action) {
         runAndWait(() -> {
             action.run();
+            //noinspection ReturnOfNull
             return null;
         });
     }
diff --git a/utility-logging-log4j/src/main/java/com/dua3/utility/logging/log4j/LogAppenderLog4j.java b/utility-logging-log4j/src/main/java/com/dua3/utility/logging/log4j/LogAppenderLog4j.java
index bda4bbe8..59da6ff4 100644
--- a/utility-logging-log4j/src/main/java/com/dua3/utility/logging/log4j/LogAppenderLog4j.java
+++ b/utility-logging-log4j/src/main/java/com/dua3/utility/logging/log4j/LogAppenderLog4j.java
@@ -121,8 +121,8 @@ public static LogAppenderLog4j createAppender(
             @PluginElement("Filters") @Nullable Filter filter) {
 
         if (name == null) {
-            LOGGER.error("No name provided for {}", APPENDER_NAME);
-            return null;
+            LOGGER.warn("No name provided for {}", APPENDER_NAME);
+            name = "[unnamed]";
         }
         if (layout == null) {
             layout = PatternLayout.createDefaultLayout();
diff --git a/utility-logging-log4j/src/main/java/com/dua3/utility/logging/log4j/LogEntryLog4J.java b/utility-logging-log4j/src/main/java/com/dua3/utility/logging/log4j/LogEntryLog4J.java
index febeb640..504139e9 100644
--- a/utility-logging-log4j/src/main/java/com/dua3/utility/logging/log4j/LogEntryLog4J.java
+++ b/utility-logging-log4j/src/main/java/com/dua3/utility/logging/log4j/LogEntryLog4J.java
@@ -5,8 +5,10 @@
 import org.apache.logging.log4j.core.LogEvent;
 import org.apache.logging.log4j.message.Message;
 import org.apache.logging.log4j.message.ReusableMessage;
+import org.jspecify.annotations.Nullable;
 
 import java.time.Instant;
+import java.util.Objects;
 import java.util.function.Supplier;
 
 /**
@@ -17,8 +19,8 @@ public final class LogEntryLog4J implements LogEntry {
     private final Instant time;
     private final LogLevel level;
     private final String marker;
-    private Supplier<String> messageFormatter;
-    private String formattedMessage;
+    private @Nullable Supplier<String> messageFormatter;
+    private @Nullable String formattedMessage;
     private final Throwable throwable;
 
     /**
@@ -58,7 +60,7 @@ public String message() {
             formattedMessage = messageFormatter.get();
             messageFormatter = null;
         }
-        return formattedMessage;
+        return Objects.requireNonNullElse(formattedMessage, "");
     }
 
     @Override
diff --git a/utility-logging-slf4j/src/main/java/com/dua3/utility/logging/slf4j/LogEntrySlf4j.java b/utility-logging-slf4j/src/main/java/com/dua3/utility/logging/slf4j/LogEntrySlf4j.java
index c86e2a64..94168bb3 100644
--- a/utility-logging-slf4j/src/main/java/com/dua3/utility/logging/slf4j/LogEntrySlf4j.java
+++ b/utility-logging-slf4j/src/main/java/com/dua3/utility/logging/slf4j/LogEntrySlf4j.java
@@ -8,6 +8,7 @@
 import org.slf4j.spi.LocationAwareLogger;
 
 import java.time.Instant;
+import java.util.Objects;
 import java.util.function.Supplier;
 
 /**
@@ -18,9 +19,9 @@ public final class LogEntrySlf4j implements LogEntry {
     private final Instant time;
     private final LogLevel level;
     private final String marker;
-    private Supplier<String> messageFormatter;
+    private @Nullable Supplier<String> messageFormatter;
     private @Nullable String formattedMessage;
-    private final Throwable throwable;
+    private final @Nullable Throwable throwable;
 
     /**
      * Creates a new instance of LogEntrySlf4j.
@@ -52,7 +53,7 @@ public String message() {
             formattedMessage = messageFormatter.get();
             messageFormatter = null;
         }
-        return formattedMessage;
+        return Objects.requireNonNullElse(formattedMessage, "");
     }
 
     @Override
@@ -106,7 +107,7 @@ public String marker() {
      * @return the throwable associated with this log entry.
      */
     @Override
-    public Throwable throwable() {
+    public @Nullable Throwable throwable() {
         return throwable;
     }
 
diff --git a/utility-logging-slf4j/src/main/java/com/dua3/utility/logging/slf4j/LoggerFactorySlf4j.java b/utility-logging-slf4j/src/main/java/com/dua3/utility/logging/slf4j/LoggerFactorySlf4j.java
index 06cf5abf..ce6a6a15 100644
--- a/utility-logging-slf4j/src/main/java/com/dua3/utility/logging/slf4j/LoggerFactorySlf4j.java
+++ b/utility-logging-slf4j/src/main/java/com/dua3/utility/logging/slf4j/LoggerFactorySlf4j.java
@@ -54,7 +54,7 @@ public class LoggerFactorySlf4j implements ILoggerFactory, LogEntryDispatcher {
     private final List<Pair<String, Level>> prefixes = new ArrayList<>();
     private final List<WeakReference<LogEntryHandler>> handlers = new ArrayList<>();
 
-    private final LogEntryHandler defaultHandler;
+    private final @Nullable LogEntryHandler defaultHandler;
     private volatile LogEntryFilter filter = LogEntryFilter.ALL_PASS_FILTER;
 
     /**
@@ -183,7 +183,7 @@ public Collection<LogEntryHandler> getLogEntryHandlers() {
      *
      * @return the default log entry handler
      */
-    public LogEntryHandler getDefaultHandler() {
-        return defaultHandler;
+    public Optional<LogEntryHandler> getDefaultHandler() {
+        return Optional.ofNullable(defaultHandler);
     }
 }
diff --git a/utility-logging-slf4j/src/main/java/com/dua3/utility/logging/slf4j/LoggerSlf4j.java b/utility-logging-slf4j/src/main/java/com/dua3/utility/logging/slf4j/LoggerSlf4j.java
index 5aa885d6..22b6fa66 100644
--- a/utility-logging-slf4j/src/main/java/com/dua3/utility/logging/slf4j/LoggerSlf4j.java
+++ b/utility-logging-slf4j/src/main/java/com/dua3/utility/logging/slf4j/LoggerSlf4j.java
@@ -56,7 +56,7 @@ public static void setDefaultLevel(Level level) {
     }
 
     @Override
-    protected String getFullyQualifiedCallerName() {
+    protected @Nullable String getFullyQualifiedCallerName() {
         return null;
     }
 
diff --git a/utility-logging/src/main/java/com/dua3/utility/logging/LogEntry.java b/utility-logging/src/main/java/com/dua3/utility/logging/LogEntry.java
index 9aa9f701..0eb18337 100644
--- a/utility-logging/src/main/java/com/dua3/utility/logging/LogEntry.java
+++ b/utility-logging/src/main/java/com/dua3/utility/logging/LogEntry.java
@@ -1,5 +1,7 @@
 package com.dua3.utility.logging;
 
+import org.jspecify.annotations.Nullable;
+
 import java.io.IOException;
 import java.io.PrintWriter;
 import java.io.StringWriter;
@@ -51,7 +53,7 @@ public interface LogEntry {
      *
      * @return the throwable object associated with this LogEntry, or null if no throwable is present
      */
-    Throwable throwable();
+    @Nullable Throwable throwable();
 
     /**
      * Formats the log entry with the given prefix and suffix.
diff --git a/utility-logging/src/main/java/com/dua3/utility/logging/LogUtil.java b/utility-logging/src/main/java/com/dua3/utility/logging/LogUtil.java
index dd8bab8d..38b175ec 100644
--- a/utility-logging/src/main/java/com/dua3/utility/logging/LogUtil.java
+++ b/utility-logging/src/main/java/com/dua3/utility/logging/LogUtil.java
@@ -16,7 +16,7 @@ private LogUtil() {
 
     private static final Logger LOG = LogManager.getLogger(LogUtil.class);
 
-    private @Nullable static LogEntryDispatcher globalDispatcher;
+    private static @Nullable LogEntryDispatcher globalDispatcher;
 
     private static synchronized void init() {
         if (globalDispatcher == null) {
@@ -60,6 +60,7 @@ public static void assureInitialized() {
      */
     public static LogEntryDispatcher getGlobalDispatcher() {
         assureInitialized();
+        assert globalDispatcher != null;
         return globalDispatcher;
     }
 }
diff --git a/utility-swing/src/main/java/com/dua3/utility/swing/ComboBoxEx.java b/utility-swing/src/main/java/com/dua3/utility/swing/ComboBoxEx.java
index dfefc7d4..ec7d7818 100644
--- a/utility-swing/src/main/java/com/dua3/utility/swing/ComboBoxEx.java
+++ b/utility-swing/src/main/java/com/dua3/utility/swing/ComboBoxEx.java
@@ -1,5 +1,6 @@
 package com.dua3.utility.swing;
 
+import com.dua3.utility.lang.LangUtil;
 import org.jspecify.annotations.Nullable;
 import org.apache.logging.log4j.Logger;
 import org.apache.logging.log4j.LogManager;
@@ -23,6 +24,7 @@
 import java.util.ArrayList;
 import java.util.Comparator;
 import java.util.List;
+import java.util.Objects;
 import java.util.Optional;
 import java.util.function.BiPredicate;
 import java.util.function.Function;
@@ -44,9 +46,9 @@ public class ComboBoxEx<T> extends JPanel {
     private final Function<T, String> format;
     private final DefaultComboBoxModel<T> model;
     private final JComboBox<T> comboBox;
-    private final JButton buttonEdit;
-    private final JButton buttonAdd;
-    private final JButton buttonRemove;
+    private final @Nullable JButton buttonEdit;
+    private final @Nullable JButton buttonAdd;
+    private final @Nullable JButton buttonRemove;
 
     /**
      * Constructs a ComboBoxEx with optional editing, adding, and removing functionality.
@@ -143,12 +145,23 @@ public Component getListCellRendererComponent(JList<?> list, @Nullable Object va
     }
 
     private void updateButtonStates() {
-        buttonEdit.setEnabled(model.getSelectedItem() != null);
-        buttonAdd.setEnabled(true);
-        buttonRemove.setEnabled(model.getSize() > 1 && model.getSelectedItem() != null);
+        if (buttonEdit != null) {
+            buttonEdit.setEnabled(model.getSelectedItem() != null);
+        }
+        if (buttonAdd != null) {
+            buttonAdd.setEnabled(true);
+        }
+        if (buttonRemove != null) {
+            buttonRemove.setEnabled(model.getSize() > 1 && model.getSelectedItem() != null);
+        }
     }
 
     private void editItem() {
+        if (edit == null) {
+            LOG.warn("editing not supported");
+            return;
+        }
+
         int idx = comboBox.getSelectedIndex();
         if (idx >= 0) {
             T item = model.getElementAt(idx);
@@ -163,7 +176,7 @@ private void editItem() {
     }
 
     private void addItem() {
-        Optional.ofNullable(add.get()).ifPresent(item -> {
+        Optional.ofNullable(add).map(Supplier::get).ifPresent(item -> {
             model.addElement(item);
             model.setSelectedItem(item);
             sortItems();
diff --git a/utility-swing/src/main/java/com/dua3/utility/swing/SwingLogPane.java b/utility-swing/src/main/java/com/dua3/utility/swing/SwingLogPane.java
index a93d65b7..506fba32 100644
--- a/utility-swing/src/main/java/com/dua3/utility/swing/SwingLogPane.java
+++ b/utility-swing/src/main/java/com/dua3/utility/swing/SwingLogPane.java
@@ -40,6 +40,7 @@
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.Objects;
 import java.util.function.Function;
 
 /**
@@ -426,7 +427,7 @@ public String get(LogEntry entry) {
         THROWABLE {
             @Override
             public String get(LogEntry entry) {
-                return entry.throwable().toString();
+                return Objects.toString(entry.throwable());
             }
         };
 
diff --git a/utility-swing/src/main/java/com/dua3/utility/swing/SwingUtil.java b/utility-swing/src/main/java/com/dua3/utility/swing/SwingUtil.java
index 165744cb..00446dfc 100644
--- a/utility-swing/src/main/java/com/dua3/utility/swing/SwingUtil.java
+++ b/utility-swing/src/main/java/com/dua3/utility/swing/SwingUtil.java
@@ -5,6 +5,7 @@
 
 package com.dua3.utility.swing;
 
+import org.jspecify.annotations.NonNull;
 import org.jspecify.annotations.Nullable;
 import com.dua3.utility.data.Color;
 import com.dua3.utility.data.Pair;
@@ -358,7 +359,7 @@ public static Optional<Path> showOpenDialog(Component parent, Path current, int
 
     @SafeVarargs
     private static Optional<Path> showFileDialog(Component parent, Path current, int selectionMode, BiFunction<? super JFileChooser, ? super Component, Integer> showDialog,
-                                                 Pair<String, String[]>... types) {
+                                                 Pair<@NonNull String, @NonNull String @NonNull[]>... types) {
         File file;
         try {
             file = current.toFile().getAbsoluteFile();
@@ -368,7 +369,7 @@ private static Optional<Path> showFileDialog(Component parent, Path current, int
         }
 
         JFileChooser jfc = new JFileChooser();
-        for (Pair<String, String[]> entry : types) {
+        for (var entry : types) {
             jfc.addChoosableFileFilter(new FileNameExtensionFilter(entry.first(), entry.second()));
         }
 
diff --git a/utility/src/main/java/com/dua3/utility/concurrent/ThreadFactoryBuilder.java b/utility/src/main/java/com/dua3/utility/concurrent/ThreadFactoryBuilder.java
index 2ed9729a..c7e8071f 100644
--- a/utility/src/main/java/com/dua3/utility/concurrent/ThreadFactoryBuilder.java
+++ b/utility/src/main/java/com/dua3/utility/concurrent/ThreadFactoryBuilder.java
@@ -9,7 +9,7 @@
  * A builder class for creating customized ThreadFactory instances.
  */
 public class ThreadFactoryBuilder {
-    private ThreadGroup group = null;
+    private @Nullable ThreadGroup group = null;
     private long stackSize = 0;
     private String prefix = "";
     private boolean daemon = false;
@@ -93,7 +93,7 @@ public ThreadFactory build() {
     }
 
     private static class CustomThreadFactory implements ThreadFactory {
-        private final ThreadGroup group;
+        private final @Nullable ThreadGroup group;
         private final long stackSize;
         private final String prefix;
         private final boolean daemon;
diff --git a/utility/src/main/java/com/dua3/utility/data/DataUtil.java b/utility/src/main/java/com/dua3/utility/data/DataUtil.java
index b1617b79..c3900706 100644
--- a/utility/src/main/java/com/dua3/utility/data/DataUtil.java
+++ b/utility/src/main/java/com/dua3/utility/data/DataUtil.java
@@ -63,7 +63,7 @@ private DataUtil() {
      * @param <T>         target type
      * @return the object converted to the target class
      */
-    public static <T> T convert(@Nullable Object value, Class<T> targetClass) {
+    public static <T extends @Nullable Object> T convert(@Nullable Object value, Class<T> targetClass) {
         return convert(value, targetClass, false);
     }
 
@@ -314,7 +314,8 @@ public static <T, U> U[] convertToArray(Collection<T> data, Class<? extends U> t
      * @return array containing the converted elements
      */
     @SuppressWarnings("unchecked")
-    public static <T, U> U[] convertToArray(Collection<T> data, Class<U> targetClass, boolean useConstructor) {
+    public static <T extends @Nullable Object, U extends @Nullable Object> U[] convertToArray(Collection<T> data, Class<U> targetClass, boolean useConstructor) {
+        //noinspection DataFlowIssue - false positive
         return data.stream()
                 .map(obj -> convert(obj, targetClass, useConstructor))
                 .toArray(n -> (U[]) Array.newInstance(targetClass, n));
@@ -373,7 +374,8 @@ public static <T, U> List<U> convert(Collection<T> data, Class<U> targetClass) {
      * @param <U>            the element target type
      * @return list containing the converted elements
      */
-    public static <T, U> List<U> convert(Collection<T> data, Class<U> targetClass, boolean useConstructor) {
+    public static <T extends @Nullable Object, U extends @Nullable Object> List<U> convert(Collection<T> data, Class<U> targetClass, boolean useConstructor) {
+        //noinspection DataFlowIssue - false positive
         return data.stream()
                 .map(obj -> convert(obj, targetClass, useConstructor))
                 .collect(Collectors.toList());
diff --git a/utility/src/main/java/com/dua3/utility/data/FileTreeNode.java b/utility/src/main/java/com/dua3/utility/data/FileTreeNode.java
index 07656f24..8364d04a 100644
--- a/utility/src/main/java/com/dua3/utility/data/FileTreeNode.java
+++ b/utility/src/main/java/com/dua3/utility/data/FileTreeNode.java
@@ -1,5 +1,6 @@
 package com.dua3.utility.data;
 
+import com.dua3.utility.lang.LangUtil;
 import org.jspecify.annotations.Nullable;
 
 import java.io.IOException;
@@ -117,6 +118,7 @@ public Stream<T> stream() {
 
     @Override
     public T parent() {
+        LangUtil.check(parent != null, "parent() called on root node");
         return parent;
     }
 
diff --git a/utility/src/main/java/com/dua3/utility/data/Pair.java b/utility/src/main/java/com/dua3/utility/data/Pair.java
index 8df72ba1..c6ead795 100644
--- a/utility/src/main/java/com/dua3/utility/data/Pair.java
+++ b/utility/src/main/java/com/dua3/utility/data/Pair.java
@@ -60,6 +60,19 @@ public static <K, V> void addToMap(Map<? super K, ? super V> m, Iterable<Pair<K,
         return new Pair<>(first, second);
     }
 
+    /**
+     * Create a Pair.
+     *
+     * @param first  the first member
+     * @param second the second member
+     * @param <T1>   type of first member
+     * @param <T2>   type of second member
+     * @return a new Pair
+     */
+    public static <T1, T2> Pair<T1, T2> ofNonNull(T1 first, T2 second) {
+        return new Pair<>(first, second);
+    }
+
     /**
      * Create a Pair.
      *
@@ -106,7 +119,7 @@ public static <K, V> void addToMap(Map<? super K, ? super V> m, Iterable<Pair<K,
      * @param f   mapper for components
      * @return Pair consisting of the mapped values of this pair
      */
-    public <U extends @Nullable Object> Pair<U, U> map(Function<Object, ? extends U> f) {
+    public <U extends @Nullable Object> Pair<U, U> map(Function<Object, ? extends @Nullable U> f) {
         return of(f.apply(first()), f.apply(second()));
     }
 
diff --git a/utility/src/main/java/com/dua3/utility/data/TreeNode.java b/utility/src/main/java/com/dua3/utility/data/TreeNode.java
index de5b69d6..7af7c627 100644
--- a/utility/src/main/java/com/dua3/utility/data/TreeNode.java
+++ b/utility/src/main/java/com/dua3/utility/data/TreeNode.java
@@ -30,7 +30,8 @@ default boolean isRoot() {
     /**
      * Get this node's parent.
      *
-     * @return this node's parent node or {@code null} if this node is a root node
+     * @return this node's parent node
+     * @throws IllegalStateException if called on the root node
      */
     N parent();
 
diff --git a/utility/src/main/java/com/dua3/utility/io/Codecs.java b/utility/src/main/java/com/dua3/utility/io/Codecs.java
index 491c004c..16e91e54 100644
--- a/utility/src/main/java/com/dua3/utility/io/Codecs.java
+++ b/utility/src/main/java/com/dua3/utility/io/Codecs.java
@@ -3,6 +3,8 @@
 import com.dua3.utility.data.Pair;
 import com.dua3.utility.data.RGBColor;
 import com.dua3.utility.lang.LangUtil;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
 import org.jspecify.annotations.NonNull;
 import org.jspecify.annotations.Nullable;
 
@@ -26,6 +28,7 @@
  * Registered codecs for a class can be obtained by using {@link #get(Class)}.
  */
 public class Codecs {
+    private static final Logger LOG  = LogManager.getLogger(Codecs.class);
 
     private final Map<String, Codec<?>> codecs = new HashMap<>();
 
@@ -93,16 +96,25 @@ public String name() {
             }
 
             @Override
-            public void encode(DataOutputStream os, C collection) throws IOException {
-                os.writeInt(collection.size());
-                for (T item : collection) {
-                    codec.encode(os, item);
+            public void encode(DataOutputStream os, @Nullable C collection) throws IOException {
+                if (collection == null) {
+                    os.writeInt(Integer.MIN_VALUE);
+                } else {
+                    os.writeInt(collection.size());
+                    for (T item : collection) {
+                        codec.encode(os, item);
+                    }
                 }
             }
 
             @Override
-            public C decode(DataInputStream is) throws IOException {
+            public @Nullable C decode(DataInputStream is) throws IOException {
                 int n = is.readInt();
+
+                if (n == Integer.MIN_VALUE) {
+                    return null;
+                }
+
                 LangUtil.check(n >= 0, "negative size for collection: %d", n);
                 C collection = construct.apply(n);
                 for (int i = 0; i < n; i++) {
@@ -153,14 +165,20 @@ public String name() {
             }
 
             @Override
-            public void encode(DataOutputStream os, M map) throws IOException {
-                ENTRIES_CODEC.encode(os, map.entrySet());
+            public void encode(DataOutputStream os, @Nullable M map) throws IOException {
+                ENTRIES_CODEC.encode(os, map == null ? null : map.entrySet());
             }
 
             @Override
-            public M decode(DataInputStream is) throws IOException {
+            public @Nullable M decode(DataInputStream is) throws IOException {
+                Collection<Map.Entry<K, V>> decoded = ENTRIES_CODEC.decode(is);
+
+                if (decoded == null) {
+                    return null;
+                }
+
                 M map = construct.get();
-                ENTRIES_CODEC.decode(is).forEach(entry -> map.put(entry.getKey(), entry.getValue()));
+                decoded.forEach(entry -> map.put(entry.getKey(), entry.getValue()));
                 return map;
             }
         };
diff --git a/utility/src/main/java/com/dua3/utility/io/CsvFormatException.java b/utility/src/main/java/com/dua3/utility/io/CsvFormatException.java
index dfce4fb0..cf9c9457 100644
--- a/utility/src/main/java/com/dua3/utility/io/CsvFormatException.java
+++ b/utility/src/main/java/com/dua3/utility/io/CsvFormatException.java
@@ -12,6 +12,8 @@
  */
 package com.dua3.utility.io;
 
+import org.jspecify.annotations.Nullable;
+
 import java.io.IOException;
 import java.io.Serial;
 import java.net.URI;
@@ -25,7 +27,7 @@ public class CsvFormatException extends IOException {
     @Serial
     private static final long serialVersionUID = 1L;
 
-    private final URI source;
+    private final @Nullable URI source;
     private final int line;
 
     /**
@@ -35,7 +37,7 @@ public class CsvFormatException extends IOException {
      * @param source  a text describing the source (preferably the filename)
      * @param line    the line number of the CSV file where the error occurred
      */
-    public CsvFormatException(String message, URI source, int line) {
+    public CsvFormatException(String message, @Nullable URI source, int line) {
         super(message);
         this.source = source;
         this.line = line;
diff --git a/utility/src/main/java/com/dua3/utility/io/CsvReader.java b/utility/src/main/java/com/dua3/utility/io/CsvReader.java
index 0799f7a0..e5a7d595 100644
--- a/utility/src/main/java/com/dua3/utility/io/CsvReader.java
+++ b/utility/src/main/java/com/dua3/utility/io/CsvReader.java
@@ -47,11 +47,11 @@ public class CsvReader extends CsvIo {
     private final RowBuilder rowBuilder;
     private final Pattern patternField;
     private final BufferedReader reader;
-    private final URI source;
+    private final @Nullable URI source;
     private int rowNumber;
     private int rowsRead;
     private int lineNumber;
-    private List<String> columnNames;
+    private @Nullable List<String> columnNames;
     private boolean ignoreExcessFields;
     private boolean ignoreMissingFields;
 
@@ -243,7 +243,7 @@ public int getRowsRead() {
      *
      * @return the source URI
      */
-    private URI getSource() {
+    private @Nullable URI getSource() {
         return source;
     }
 
diff --git a/utility/src/main/java/com/dua3/utility/io/Decoder.java b/utility/src/main/java/com/dua3/utility/io/Decoder.java
index 09309c5d..bde3531c 100644
--- a/utility/src/main/java/com/dua3/utility/io/Decoder.java
+++ b/utility/src/main/java/com/dua3/utility/io/Decoder.java
@@ -34,6 +34,7 @@ public interface Decoder<T extends @Nullable Object> {
 
         Collection<T> collection = collectionConstructor.apply(size);
         for (int i = 0; i < size; i++) {
+            //noinspection DataFlowIssue - false positive
             collection.add(codec.decode(is));
         }
 
diff --git a/utility/src/main/java/com/dua3/utility/io/FileType.java b/utility/src/main/java/com/dua3/utility/io/FileType.java
index 7991ccf1..54ca7172 100644
--- a/utility/src/main/java/com/dua3/utility/io/FileType.java
+++ b/utility/src/main/java/com/dua3/utility/io/FileType.java
@@ -38,7 +38,7 @@
  *
  * @param <T> the type corresponding to the data contained in files of this {@link FileType} instance.
  */
-public abstract class FileType<T extends @Nullable Object> implements Comparable<FileType<?>> {
+public abstract class FileType<T> implements Comparable<FileType<?>> {
 
     /**
      * Set of defined file types.
diff --git a/utility/src/main/java/com/dua3/utility/io/IoOptions.java b/utility/src/main/java/com/dua3/utility/io/IoOptions.java
index 5b5792ce..5f37ddbe 100644
--- a/utility/src/main/java/com/dua3/utility/io/IoOptions.java
+++ b/utility/src/main/java/com/dua3/utility/io/IoOptions.java
@@ -53,7 +53,7 @@ public static ChoiceOption<Locale> locale() {
                         "--locale")
                 .displayName("Locale")
                 .description("set locale")
-                .defaultValue(Locale::getDefault);
+                .defaultSupplier(Locale::getDefault);
     }
 
     /**
diff --git a/utility/src/main/java/com/dua3/utility/io/IoUtil.java b/utility/src/main/java/com/dua3/utility/io/IoUtil.java
index 164e87f4..821dcd7e 100644
--- a/utility/src/main/java/com/dua3/utility/io/IoUtil.java
+++ b/utility/src/main/java/com/dua3/utility/io/IoUtil.java
@@ -6,7 +6,6 @@
 package com.dua3.utility.io;
 
 import org.jspecify.annotations.Nullable;
-import com.dua3.utility.data.Pair;
 import com.dua3.utility.lang.LangUtil;
 import com.dua3.utility.lang.Platform;
 import com.dua3.utility.text.TextUtil;
@@ -91,7 +90,7 @@ private IoUtil() {
         // utility class
     }
 
-    private static record FileNameInfo(int idxStart, int idxEnd) {}
+    private record FileNameInfo(int idxStart, int idxEnd) {}
 
     /**
      * Extract the filename from a path given as a String. In addition to the system dependent
@@ -462,6 +461,7 @@ public static Path toPath(String s) {
      */
     public static void deleteRecursive(Path path) throws IOException {
         try (Stream<Path> files = Files.walk(path, FileVisitOption.FOLLOW_LINKS)) {
+            //noinspection DataFlowIssue - false positive
             files
                     .sorted(Comparator.reverseOrder())
                     .forEach(LangUtil.uncheckedConsumer(Files::deleteIfExists));
diff --git a/utility/src/main/java/com/dua3/utility/io/SoftResource.java b/utility/src/main/java/com/dua3/utility/io/SoftResource.java
index b71b1a90..366198f3 100644
--- a/utility/src/main/java/com/dua3/utility/io/SoftResource.java
+++ b/utility/src/main/java/com/dua3/utility/io/SoftResource.java
@@ -5,6 +5,8 @@
 
 package com.dua3.utility.io;
 
+import org.jspecify.annotations.Nullable;
+
 import java.lang.ref.SoftReference;
 import java.util.function.Supplier;
 
@@ -17,12 +19,16 @@
  */
 public final class SoftResource<T> {
 
-    private Supplier<? extends T> supplier;
+    public static final SoftReference<?> EMPTY_REFERENCE = new SoftReference<>(null);
+    public static final SoftResource<?> EMPTY_RESOURCE = new SoftResource<>(null);
+
+    private @Nullable Supplier<? extends @Nullable T> supplier;
     private SoftReference<T> ref;
 
-    private SoftResource(Supplier<? extends T> supplier) {
+    private SoftResource(@Nullable Supplier<? extends @Nullable T> supplier) {
         this.supplier = supplier;
-        this.ref = new SoftReference<>(null);
+        //noinspection unchecked
+        this.ref = (SoftReference<T>) EMPTY_REFERENCE;
     }
 
     /**
@@ -33,7 +39,7 @@ private SoftResource(Supplier<? extends T> supplier) {
      *                 invocation return equal instances
      * @return soft resource
      */
-    public static <T> SoftResource<T> of(Supplier<? extends T> supplier) {
+    public static <T> SoftResource<T> of(Supplier<? extends @Nullable T> supplier) {
         return new SoftResource<>(supplier);
     }
 
@@ -44,7 +50,8 @@ public static <T> SoftResource<T> of(Supplier<? extends T> supplier) {
      * @return empty soft resource
      */
     public static <T> SoftResource<T> emptyReference() {
-        return new SoftResource<>(null);
+        //noinspection unchecked
+        return (SoftResource<T>) EMPTY_RESOURCE;
     }
 
     /**
@@ -54,7 +61,7 @@ public static <T> SoftResource<T> emptyReference() {
      * if it has not yet been set or has been garbage collected, it will be
      * restored by invoking the supplier
      */
-    public T get() {
+    public @Nullable T get() {
         T obj = ref.get();
         if (obj == null && supplier != null) {
             obj = supplier.get();
@@ -63,6 +70,7 @@ public T get() {
                 supplier = null;
             }
 
+            //noinspection DataFlowIssue - false positive
             ref = new SoftReference<>(obj);
         }
         return obj;
@@ -91,7 +99,7 @@ public ResourceHolder<T> hold() {
     /**
      * Helper class to prevent the resource from being garbage collected.
      */
-    public static final class ResourceHolder<T> implements AutoCloseable {
+    public static final class ResourceHolder<T extends @Nullable Object> implements AutoCloseable {
         private final SoftResource<T> soft;
         private T strong;
 
diff --git a/utility/src/main/java/com/dua3/utility/lang/BatchCollector.java b/utility/src/main/java/com/dua3/utility/lang/BatchCollector.java
index dea7f7f0..e68ddf95 100644
--- a/utility/src/main/java/com/dua3/utility/lang/BatchCollector.java
+++ b/utility/src/main/java/com/dua3/utility/lang/BatchCollector.java
@@ -22,7 +22,7 @@
  * @param <T> the item type
  * @param <K> the key type
  */
-public class BatchCollector<T extends @Nullable Object, K extends @Nullable Object> implements Collector<T, Deque<Pair<K, List<T>>>, List<Pair<K, List<T>>>> {
+public class BatchCollector<T extends @Nullable Object, K> implements Collector<T, Deque<Pair<K, List<T>>>, List<Pair<K, List<T>>>> {
     private final Function<? super T, ? extends K> keyMapper;
     private final K defaultKey;
 
@@ -68,6 +68,7 @@ public BiConsumer<Deque<Pair<K, List<T>>>, T> accumulator() {
                 bucket = accu.peekLast().second();
             }
 
+            //noinspection DataFlowIssue
             bucket.add(item);
         };
     }
diff --git a/utility/src/main/java/com/dua3/utility/lang/BuildInfo.java b/utility/src/main/java/com/dua3/utility/lang/BuildInfo.java
index f7d00a3b..17f5fabe 100644
--- a/utility/src/main/java/com/dua3/utility/lang/BuildInfo.java
+++ b/utility/src/main/java/com/dua3/utility/lang/BuildInfo.java
@@ -6,6 +6,7 @@
 import java.io.IOException;
 import java.io.InputStream;
 import java.time.ZonedDateTime;
+import java.util.Objects;
 import java.util.Optional;
 import java.util.Properties;
 import java.util.regex.Matcher;
@@ -80,7 +81,7 @@ public static BuildInfo create(Properties properties) {
      */
     public static BuildInfo create(Class<?> cls, String resource) throws IOException {
         try (InputStream in = cls.getResourceAsStream(resource)) {
-            return create(LangUtil.loadProperties(in));
+            return create(LangUtil.loadProperties(Objects.requireNonNull(in, () -> "resource not found: " + resource)));
         }
     }
 
diff --git a/utility/src/main/java/com/dua3/utility/lang/LangUtil.java b/utility/src/main/java/com/dua3/utility/lang/LangUtil.java
index bdd9473e..6c175bd5 100644
--- a/utility/src/main/java/com/dua3/utility/lang/LangUtil.java
+++ b/utility/src/main/java/com/dua3/utility/lang/LangUtil.java
@@ -152,7 +152,7 @@ public static void check(boolean condition, String fmt, Object... args) {
      * @param <T> the type
      * @return a, if a != null, else b
      */
-    public static <T extends @Nullable Object> T orElse(@Nullable T a, T b) {
+    public static <T extends @Nullable Object> T orElse(T a, T b) {
         return a != null ? a : b;
     }
 
@@ -164,7 +164,7 @@ public static void check(boolean condition, String fmt, Object... args) {
      * @param <T> the type
      * @return a, if a != null, else b.get()
      */
-    public static <T extends @Nullable Object> T orElseGet(@Nullable T a, Supplier<? extends T> b) {
+    public static <T extends @Nullable Object> T orElseGet(T a, Supplier<? extends T> b) {
         return a != null ? a : b.get();
     }
 
@@ -253,7 +253,7 @@ private static RuntimeException wrapException(Exception e) {
      * @throws UncheckedIOException if {@link IOException} is thrown during execution of the argument passed
      * @throws WrappedException     if any other type of Exception is thrown during execution of the argument passed
      */
-    public static <T extends @Nullable Object, E extends Exception> Consumer<T> uncheckedConsumer(ConsumerThrows<? super T, E> c) {
+    public static <T extends @Nullable Object, E extends Exception> Consumer<T> uncheckedConsumer(ConsumerThrows<T, E> c) {
         return arg -> {
             try {
                 c.accept(arg);
@@ -301,7 +301,7 @@ private static RuntimeException wrapException(Exception e) {
      * @throws WrappedException     if any other type of Exception is thrown during execution of the argument passed
      */
     @SuppressWarnings("ProhibitedExceptionThrown")
-    public static <T extends @Nullable Object, R extends @Nullable Object, E extends Exception> Function<T, R> uncheckedFunction(FunctionThrows<? super T, ? extends R, E> f) {
+    public static <T extends @Nullable Object, R extends @Nullable Object, E extends Exception> Function<T, R> uncheckedFunction(FunctionThrows<T, R, E> f) {
         return arg -> {
             try {
                 return f.apply(arg);
@@ -477,7 +477,7 @@ public static <K, V> void putAll(Map<? super K, ? super V> map, Map.Entry<K, V>.
      * @param supplier the Supplier
      * @return caching Supplier
      */
-    public static <T extends @Nullable Object> Supplier<T> cache(Supplier<? extends T> supplier) {
+    public static <T extends @Nullable Object> Supplier<T> cache(Supplier<T> supplier) {
         return new CachingSupplier<>(supplier, t -> {});
     }
 
@@ -1135,6 +1135,7 @@ private static class LazyFormatter {
         public LazyFormatter(@Nullable String fmt, Object... args) {
             if (fmt == null) {
                 this.s = NULL_STRING;
+                //noinspection DataFlowIssue - false positive
                 this.args = null;
             } else {
                 this.s = fmt;
@@ -1142,6 +1143,7 @@ public LazyFormatter(@Nullable String fmt, Object... args) {
             }
         }
 
+        @SuppressWarnings("DataFlowIssue") // false positive
         @Override
         public String toString() {
             if (args != null) {
diff --git a/utility/src/main/java/com/dua3/utility/lang/RingBuffer.java b/utility/src/main/java/com/dua3/utility/lang/RingBuffer.java
index f39f62f2..e6445c68 100644
--- a/utility/src/main/java/com/dua3/utility/lang/RingBuffer.java
+++ b/utility/src/main/java/com/dua3/utility/lang/RingBuffer.java
@@ -12,11 +12,11 @@
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.ConcurrentModificationException;
+import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
 import java.util.NoSuchElementException;
 import java.util.Objects;
-import java.util.Set;
 
 /**
  * A ring buffer implementation.
@@ -30,7 +30,7 @@
  */
 public class RingBuffer<E extends @Nullable Object> implements Collection<E> {
 
-    private E[] data;
+    private @Nullable E[] data;
     private int entries;
     private int start;
 
@@ -41,7 +41,7 @@ public class RingBuffer<E extends @Nullable Object> implements Collection<E> {
      */
     @SuppressWarnings("unchecked")
     public RingBuffer(int capacity) {
-        data = (E[]) new Object[capacity];
+        data = (@Nullable E[]) new Object[capacity];
         start = 0;
         entries = 0;
     }
@@ -53,7 +53,7 @@ public RingBuffer(int capacity) {
      * @return true
      */
     @Override
-    public boolean add(@Nullable E item) {
+    public boolean add(E item) {
         put(item);
         return true;
     }
@@ -84,7 +84,7 @@ public boolean remove(@Nullable Object o) {
 
     @Override
     public boolean containsAll(Collection<?> c) {
-        return Set.of(toArray()).containsAll(c);
+        return new HashSet<>(this).containsAll(c);
     }
 
     /**
@@ -213,7 +213,7 @@ public Object[] toArray() {
 
     @Override
     @SuppressWarnings("unchecked")
-    public <T> T[] toArray(T[] a) {
+    public <T> @Nullable T[] toArray(@Nullable T[] a) {
         if (a.length < entries) {
             a = (T[]) java.lang.reflect.Array.newInstance(a.getClass().getComponentType(), entries);
         }
@@ -306,6 +306,7 @@ public List<E> subList(int fromIndex, int toIndex) {
         int sz = toIndex - fromIndex;
         Objects.checkFromIndexSize(fromIndex, sz, len);
 
+        //noinspection NullableProblems
         return new AbstractList<>() {
             @Override
             public E get(int index) {
diff --git a/utility/src/main/java/com/dua3/utility/options/Arguments.java b/utility/src/main/java/com/dua3/utility/options/Arguments.java
index e3aa22bb..0dfbea26 100644
--- a/utility/src/main/java/com/dua3/utility/options/Arguments.java
+++ b/utility/src/main/java/com/dua3/utility/options/Arguments.java
@@ -125,7 +125,7 @@ public void validate(
         options.forEach(entry -> hist.compute(entry.option, (k_, i_) -> i_ == null ? 1 : i_ + 1));
 
         allOptions.stream()
-                .map(option -> Pair.of(option, hist.getOrDefault(option, 0)))
+                .map(option -> Pair.ofNonNull(option, hist.getOrDefault(option, 0)))
                 .forEach(p -> {
                     Option<?> option = p.first();
                     int occurrences = p.second();
diff --git a/utility/src/main/java/com/dua3/utility/options/ArgumentsParserBuilder.java b/utility/src/main/java/com/dua3/utility/options/ArgumentsParserBuilder.java
index 5402217f..0820ff76 100644
--- a/utility/src/main/java/com/dua3/utility/options/ArgumentsParserBuilder.java
+++ b/utility/src/main/java/com/dua3/utility/options/ArgumentsParserBuilder.java
@@ -2,6 +2,7 @@
 
 import com.dua3.utility.data.DataUtil;
 import com.dua3.utility.lang.LangUtil;
+import org.jspecify.annotations.Nullable;
 
 import java.util.LinkedHashMap;
 import java.util.Map;
@@ -108,7 +109,7 @@ public Flag flag(String... names) {
      * @param names  the names for the option, at least one
      * @return the created SimpleOption
      */
-    public <T> SimpleOption<T> simpleOption(Class<? extends T> type, String... names) {
+    public <T extends @Nullable Object> SimpleOption<T> simpleOption(Class<? extends T> type, String... names) {
         return simpleOption(s -> DataUtil.convert(s, type, true), names);
     }
 
@@ -120,7 +121,7 @@ public <T> SimpleOption<T> simpleOption(Class<? extends T> type, String... names
      * @param names  the names for the option, at least one.
      * @return the created SimpleOption.
      */
-    public <T> SimpleOption<T> simpleOption(Function<String, ? extends T> mapper, String... names) {
+    public <T extends @Nullable Object> SimpleOption<T> simpleOption(Function<String, ? extends T> mapper, String... names) {
         return addOption(SimpleOption.create(mapper, names));
     }
 
@@ -144,7 +145,7 @@ public <E extends Enum<E>> ChoiceOption<E> choiceOption(Class<? extends E> enumC
      * @param names  the names for the option, at least one.
      * @return the created StandardOption.
      */
-    public <T> StandardOption<T> option(Class<? extends T> type, String... names) {
+    public <T extends @Nullable Object> StandardOption<T> option(Class<? extends T> type, String... names) {
         return option(s -> DataUtil.convert(s, type, true), names);
     }
 
@@ -156,7 +157,7 @@ public <T> StandardOption<T> option(Class<? extends T> type, String... names) {
      * @param names  the names for the option, at least one.
      * @return the created StandardOption.
      */
-    public <T> StandardOption<T> option(Function<String, ? extends T> mapper, String... names) {
+    public <T extends @Nullable Object> StandardOption<T> option(Function<String, ? extends T> mapper, String... names) {
         return addOption(StandardOption.create(mapper, names));
     }
 
diff --git a/utility/src/main/java/com/dua3/utility/options/ChoiceOption.java b/utility/src/main/java/com/dua3/utility/options/ChoiceOption.java
index 7926bca8..e67d9497 100644
--- a/utility/src/main/java/com/dua3/utility/options/ChoiceOption.java
+++ b/utility/src/main/java/com/dua3/utility/options/ChoiceOption.java
@@ -19,7 +19,7 @@
 public final class ChoiceOption<T extends @Nullable Object> extends Option<T> {
 
     private final Supplier<? extends Collection<? extends T>> values;
-    private Supplier<? extends @Nullable T> defaultValue = () -> null;
+    private Supplier<? extends @Nullable T> defaultSupplier = () -> null;
 
     /**
      * Constructor.
@@ -143,17 +143,17 @@ public ChoiceOption<T> handler(Consumer<Collection<T>> handler) {
      * @return this option
      */
     public ChoiceOption<T> defaultValue(@Nullable T defaultValue) {
-        return defaultValue(() -> defaultValue);
+        return defaultSupplier(() -> defaultValue);
     }
 
     /**
      * Set default value.
      *
-     * @param defaultValue the default value
+     * @param defaultSupplier the default value
      * @return this option
      */
-    public ChoiceOption<T> defaultValue(Supplier<? extends T> defaultValue) {
-        this.defaultValue = defaultValue;
+    public ChoiceOption<T> defaultSupplier(Supplier<? extends @Nullable T> defaultSupplier) {
+        this.defaultSupplier = defaultSupplier;
         return this;
     }
 
@@ -179,7 +179,7 @@ public ChoiceOption<T> argName(String argName) {
      * @return Optional holding the default value.
      */
     public Optional<T> getDefault() {
-        return Optional.ofNullable(defaultValue.get());
+        return Optional.ofNullable(defaultSupplier.get());
     }
 
     /**
diff --git a/utility/src/main/java/com/dua3/utility/options/SimpleOption.java b/utility/src/main/java/com/dua3/utility/options/SimpleOption.java
index 525b7b6e..27f1d2fa 100644
--- a/utility/src/main/java/com/dua3/utility/options/SimpleOption.java
+++ b/utility/src/main/java/com/dua3/utility/options/SimpleOption.java
@@ -18,7 +18,7 @@
  */
 public final class SimpleOption<T extends @Nullable Object> extends Option<T> {
 
-    private Supplier<? extends T> defaultValue = () -> null;
+    private Supplier<? extends @Nullable T> defaultSupplier = () -> null;
 
     /**
      * Construct a new simple option with the given name(s).
@@ -93,17 +93,17 @@ public SimpleOption<T> handler(Consumer<Collection<T>> handler) {
      * @return this option
      */
     public SimpleOption<T> defaultValue(@Nullable T defaultValue) {
-        return defaultValue(() -> defaultValue);
+        return defaultSupplier(() -> defaultValue);
     }
 
     /**
      * Set default value.
      *
-     * @param defaultValue the default value
+     * @param defaultSupplier the default value
      * @return this option
      */
-    public SimpleOption<T> defaultValue(Supplier<? extends T> defaultValue) {
-        this.defaultValue = defaultValue;
+    public SimpleOption<T> defaultSupplier(Supplier<? extends T> defaultSupplier) {
+        this.defaultSupplier = defaultSupplier;
         return this;
     }
 
@@ -124,7 +124,7 @@ public SimpleOption<T> required() {
      */
     @Override
     public Optional<T> getDefault() {
-        return Optional.ofNullable(defaultValue.get());
+        return Optional.ofNullable(defaultSupplier.get());
     }
 
 }
diff --git a/utility/src/main/java/com/dua3/utility/spi/SpiLoader.java b/utility/src/main/java/com/dua3/utility/spi/SpiLoader.java
index 9510f4ad..25512fcb 100644
--- a/utility/src/main/java/com/dua3/utility/spi/SpiLoader.java
+++ b/utility/src/main/java/com/dua3/utility/spi/SpiLoader.java
@@ -82,7 +82,7 @@ public LoaderBuilder<T> defaultSupplier(Supplier<? extends T> defaultSupplier) {
          */
         public SpiLoader<T> build() {
             Predicate<T> p = predicate != null ? predicate : t -> true;
-            Supplier<? extends T> d = defaultSupplier != null ? defaultSupplier : () -> null;
+            Supplier<? extends @Nullable T> d = defaultSupplier != null ? defaultSupplier : () -> null;
             ClassLoader c = cl != null ? cl : ClassLoader.getSystemClassLoader();
 
             return new SpiLoader<>(type, c, p, d);
diff --git a/utility/src/main/java/com/dua3/utility/text/AnsiConverter.java b/utility/src/main/java/com/dua3/utility/text/AnsiConverter.java
index 2535f849..38d64c5a 100644
--- a/utility/src/main/java/com/dua3/utility/text/AnsiConverter.java
+++ b/utility/src/main/java/com/dua3/utility/text/AnsiConverter.java
@@ -2,6 +2,7 @@
 
 import com.dua3.utility.data.Pair;
 import com.dua3.utility.io.AnsiCode;
+import org.jspecify.annotations.Nullable;
 
 import java.util.ArrayDeque;
 import java.util.Collection;
@@ -18,7 +19,7 @@
 public final class AnsiConverter extends AttributeBasedConverter<String> {
 
     private static final Map<String, Object> DEFAULT_ATTRIBUTES = new HashMap<>();
-    private final HashMap<String, BiFunction<Object, Object, String>> mappings = new HashMap<>();
+    private final HashMap<String, BiFunction<@Nullable Object, @Nullable Object, String>> mappings = new HashMap<>();
     private boolean reset;
     private boolean reverseVideo;
 
@@ -110,12 +111,12 @@ protected String get() {
         }
 
         @Override
-        protected void apply(Map<String, Pair<Object, Object>> changedAttributes) {
-            Map<String, Object> attributes = new HashMap<>();
+        protected void apply(Map<String, Pair<@Nullable Object, @Nullable Object>> changedAttributes) {
+            Map<String, @Nullable Object> attributes = new HashMap<>();
             Deque<String> tags = new ArrayDeque<>();
             changedAttributes.forEach((attribute, values) -> {
                 attributes.put(attribute, values.second());
-                BiFunction<Object, Object, String> mapping = mappings.get(attribute);
+                BiFunction<@Nullable Object, @Nullable Object, String> mapping = mappings.get(attribute);
                 if (mapping != null) {
                     tags.push(mapping.apply(values.first(), values.second()));
                 }
diff --git a/utility/src/main/java/com/dua3/utility/text/AttributeBasedConverter.java b/utility/src/main/java/com/dua3/utility/text/AttributeBasedConverter.java
index 1812caf5..cfefe6e8 100644
--- a/utility/src/main/java/com/dua3/utility/text/AttributeBasedConverter.java
+++ b/utility/src/main/java/com/dua3/utility/text/AttributeBasedConverter.java
@@ -18,7 +18,7 @@
  *
  * @param <T> target type of conversion
  */
-public abstract class AttributeBasedConverter<T extends @Nullable Object> implements RichTextConverter<T> {
+public abstract class AttributeBasedConverter<T> implements RichTextConverter<T> {
 
     /**
      * Factory method to create a compatible converter implementation instance for this converter.
@@ -124,7 +124,7 @@ private static void copyAttributes(Iterable<? extends Map.Entry<String, @Nullabl
          */
         protected void setStyle(Run run) {
             // collect this run's attribute
-            Map<String, Object> newAttributes = collectAttributes(run);
+            Map<String, @Nullable Object> newAttributes = collectAttributes(run);
             handleAttributeChanges(newAttributes);
         }
 
diff --git a/utility/src/main/java/com/dua3/utility/text/AttributedCharacter.java b/utility/src/main/java/com/dua3/utility/text/AttributedCharacter.java
index 3e81575f..4adfe03e 100644
--- a/utility/src/main/java/com/dua3/utility/text/AttributedCharacter.java
+++ b/utility/src/main/java/com/dua3/utility/text/AttributedCharacter.java
@@ -49,6 +49,8 @@ public TextAttributes attributes() {
      */
     @SuppressWarnings("unchecked")
     default List<Style> getStyles() {
-        return (List<Style>) attributes().getOrDefault(RichText.ATTRIBUTE_NAME_STYLE_LIST, Collections.emptyList());
+        List<Style> list = (List<Style>) attributes().getOrDefault(RichText.ATTRIBUTE_NAME_STYLE_LIST, Collections.emptyList());
+        assert list != null;
+        return list;
     }
 }
diff --git a/utility/src/main/java/com/dua3/utility/text/ComparisonSettings.java b/utility/src/main/java/com/dua3/utility/text/ComparisonSettings.java
index c05cf973..874ca6f9 100644
--- a/utility/src/main/java/com/dua3/utility/text/ComparisonSettings.java
+++ b/utility/src/main/java/com/dua3/utility/text/ComparisonSettings.java
@@ -1,5 +1,7 @@
 package com.dua3.utility.text;
 
+import org.jspecify.annotations.Nullable;
+
 import java.util.function.Function;
 
 /**
@@ -16,7 +18,7 @@
  * @param ignoreItalic whether to ignore difference in italics
  */
 public record ComparisonSettings(
-        Function<String, String> fontMapper,
+        Function<@Nullable String, @Nullable String> fontMapper,
         boolean ignoreCase,
         boolean ignoreFontFamily,
         boolean ignoreFontSize,
diff --git a/utility/src/main/java/com/dua3/utility/text/FontDef.java b/utility/src/main/java/com/dua3/utility/text/FontDef.java
index 36d7dd9a..a262a347 100644
--- a/utility/src/main/java/com/dua3/utility/text/FontDef.java
+++ b/utility/src/main/java/com/dua3/utility/text/FontDef.java
@@ -254,7 +254,7 @@ private static boolean nullOrEquals(@Nullable Object a, @Nullable Object b) {
     }
 
     // a little helper for the consumeIfDefined... methods
-    private static <T extends @Nullable Object> boolean consumeIfDefined(@Nullable T v, Consumer<T> c) {
+    private static <T> boolean consumeIfDefined(@Nullable T v, Consumer<T> c) {
         boolean run = v != null;
         if (run) {
             c.accept(v);
@@ -465,7 +465,7 @@ public void merge(FontDef delta) {
      *
      * @param c consumer to run if the attribute value is defined. It is called with the attribute value as argument
      */
-    public void ifColorDefined(Consumer<? super @Nullable Color> c) {
+    public void ifColorDefined(Consumer<? super Color> c) {
         consumeIfDefined(color, c);
     }
 
@@ -475,7 +475,7 @@ public void ifColorDefined(Consumer<? super @Nullable Color> c) {
      * @param c consumer to run if the attribute value is defined. It is called with the attribute value as argument
      * @return true, if the action was run
      */
-    public boolean ifSizeDefined(Consumer<? super @Nullable Float> c) {
+    public boolean ifSizeDefined(Consumer<? super Float> c) {
         return consumeIfDefined(size, c);
     }
 
@@ -485,7 +485,7 @@ public boolean ifSizeDefined(Consumer<? super @Nullable Float> c) {
      * @param c consumer to run if the attribute value is defined. It is called with the attribute value as argument
      * @return true, if the action was run
      */
-    public boolean ifFamilyDefined(Consumer<? super @Nullable String> c) {
+    public boolean ifFamilyDefined(Consumer<? super String> c) {
         return consumeIfDefined(family, c);
     }
 
@@ -494,7 +494,7 @@ public boolean ifFamilyDefined(Consumer<? super @Nullable String> c) {
      *
      * @param c consumer to run if the attribute value is defined. It is called with the attribute value as argument
      */
-    public void ifBoldDefined(Consumer<? super @Nullable Boolean> c) {
+    public void ifBoldDefined(Consumer<? super Boolean> c) {
         consumeIfDefined(bold, c);
     }
 
@@ -503,7 +503,7 @@ public void ifBoldDefined(Consumer<? super @Nullable Boolean> c) {
      *
      * @param c consumer to run if the attribute value is defined. It is called with the attribute value as argument
      */
-    public void ifItalicDefined(Consumer<? super @Nullable Boolean> c) {
+    public void ifItalicDefined(Consumer<? super Boolean> c) {
         consumeIfDefined(italic, c);
     }
 
@@ -512,7 +512,7 @@ public void ifItalicDefined(Consumer<? super @Nullable Boolean> c) {
      *
      * @param c consumer to run if the attribute value is defined. It is called with the attribute value as argument
      */
-    public void ifUnderlineDefined(Consumer<? super @Nullable Boolean> c) {
+    public void ifUnderlineDefined(Consumer<? super Boolean> c) {
         consumeIfDefined(underline, c);
     }
 
@@ -521,7 +521,7 @@ public void ifUnderlineDefined(Consumer<? super @Nullable Boolean> c) {
      *
      * @param c consumer to run if the attribute value is defined. It is called with the attribute value as argument
      */
-    public void ifStrikeThroughDefined(Consumer<? super @Nullable Boolean> c) {
+    public void ifStrikeThroughDefined(Consumer<? super Boolean> c) {
         consumeIfDefined(strikeThrough, c);
     }
 
diff --git a/utility/src/main/java/com/dua3/utility/text/HtmlConverter.java b/utility/src/main/java/com/dua3/utility/text/HtmlConverter.java
index 8fd79301..1ac65015 100644
--- a/utility/src/main/java/com/dua3/utility/text/HtmlConverter.java
+++ b/utility/src/main/java/com/dua3/utility/text/HtmlConverter.java
@@ -1,5 +1,7 @@
 package com.dua3.utility.text;
 
+import org.jspecify.annotations.Nullable;
+
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.HashMap;
@@ -23,7 +25,7 @@ public final class HtmlConverter extends TagBasedConverter<String> {
      * Value: the function that maps values to tags
      */
     private final Map<String, Function<Object, HtmlTag>> mappings = new HashMap<>();
-    private UnaryOperator<Map<String, Object>> refineStyleProperties = m -> m;
+    private UnaryOperator<Map<String, @Nullable Object>> refineStyleProperties = m -> m;
     /**
      * The default mapper used to generate tags for attributes without mapping.
      */
@@ -312,7 +314,7 @@ protected void appendClosingTags(List<Style> styles) {
 
         private List<HtmlTag> getTags(List<Style> styles) {
             List<HtmlTag> tags = new ArrayList<>();
-            Map<String, Object> properties = new LinkedHashMap<>();
+            Map<String, @Nullable Object> properties = new LinkedHashMap<>();
             for (Style style : styles) {
                 style.stream().forEach(entry -> properties.put(entry.getKey(), entry.getValue()));
             }
diff --git a/utility/src/main/java/com/dua3/utility/text/RichText.java b/utility/src/main/java/com/dua3/utility/text/RichText.java
index 5e6d7931..be39a79a 100644
--- a/utility/src/main/java/com/dua3/utility/text/RichText.java
+++ b/utility/src/main/java/com/dua3/utility/text/RichText.java
@@ -555,7 +555,7 @@ public boolean tryAdvance(Consumer<? super RichText> action) {
             }
 
             @Override
-            public Spliterator<RichText> trySplit() {
+            public @Nullable Spliterator<RichText> trySplit() {
                 return null;
             }
 
diff --git a/utility/src/main/java/com/dua3/utility/text/RichTextBuilder.java b/utility/src/main/java/com/dua3/utility/text/RichTextBuilder.java
index 15ac5e4d..2aee796e 100644
--- a/utility/src/main/java/com/dua3/utility/text/RichTextBuilder.java
+++ b/utility/src/main/java/com/dua3/utility/text/RichTextBuilder.java
@@ -198,8 +198,8 @@ public int length() {
     @SuppressWarnings("unchecked")
     void appendRun(Run run) {
         // set attributes
-        Map<String, Object> attributes = split();
-        Map<String, Object> backup = new HashMap<>();
+        Map<String, @Nullable Object> attributes = split();
+        Map<String, @Nullable Object> backup = new HashMap<>();
         for (Entry<String, Object> entry : run.getAttributes().entrySet()) {
             String key = entry.getKey();
             Object value = entry.getValue();
diff --git a/utility/src/main/java/com/dua3/utility/text/Run.java b/utility/src/main/java/com/dua3/utility/text/Run.java
index 9d815bfd..09c03e01 100644
--- a/utility/src/main/java/com/dua3/utility/text/Run.java
+++ b/utility/src/main/java/com/dua3/utility/text/Run.java
@@ -182,6 +182,7 @@ public TextAttributes attributes() {
      */
     @SuppressWarnings("unchecked")
     public List<Style> getStyles() {
+        //noinspection DataFlowIssue - false positive
         return (List<Style>) attributes().getOrDefault(RichText.ATTRIBUTE_NAME_STYLE_LIST, Collections.emptyList());
     }
 
diff --git a/utility/src/main/java/com/dua3/utility/text/StandardFontMapper.java b/utility/src/main/java/com/dua3/utility/text/StandardFontMapper.java
index ca2d849b..52e9a6f6 100644
--- a/utility/src/main/java/com/dua3/utility/text/StandardFontMapper.java
+++ b/utility/src/main/java/com/dua3/utility/text/StandardFontMapper.java
@@ -1,7 +1,5 @@
 package com.dua3.utility.text;
 
-import org.jspecify.annotations.Nullable;
-
 import java.util.function.Function;
 import java.util.regex.Pattern;
 
@@ -48,14 +46,11 @@ public enum StandardFontMapper implements Function<String, String> {
      */
     IGNORE_SUBSETS_AND_KNOWN_ALIASES(StandardFontMapper::removeSubsetTagAndReplaceKnownAliases);
 
-    private static String removeSubsetTagAndReplaceKnownAliases(@Nullable String s) {
+    private static String removeSubsetTagAndReplaceKnownAliases(String s) {
         return replaceKnownAliases(removeSubsetTag(s));
     }
 
-    private static String replaceKnownAliases(@Nullable String s) {
-        if (s == null) {
-            return null;
-        }
+    private static String replaceKnownAliases(String s) {
         return switch (s) {
             case "ArialMT" -> "Arial";
             case "TimesNewRomanPSMT", "Times-Roman" -> "Times New Roman";
@@ -66,8 +61,8 @@ private static String replaceKnownAliases(@Nullable String s) {
 
     private static final Pattern PATTERN_SUBSET_TAG = Pattern.compile("^[A-Z]{6}\\+");
 
-    private static String removeSubsetTag(@Nullable String s) {
-        return s == null ? null : PATTERN_SUBSET_TAG.matcher(s).replaceFirst("");
+    private static String removeSubsetTag(String s) {
+        return PATTERN_SUBSET_TAG.matcher(s).replaceFirst("");
     }
 
     private final Function<? super String, String> mapper;
@@ -77,7 +72,7 @@ private static String removeSubsetTag(@Nullable String s) {
     }
 
     @Override
-    public String apply(@Nullable String s) {
+    public String apply(String s) {
         return mapper.apply(s);
     }
 }
\ No newline at end of file
diff --git a/utility/src/main/java/com/dua3/utility/text/Style.java b/utility/src/main/java/com/dua3/utility/text/Style.java
index 9fe546e1..2dfa8e31 100644
--- a/utility/src/main/java/com/dua3/utility/text/Style.java
+++ b/utility/src/main/java/com/dua3/utility/text/Style.java
@@ -5,6 +5,7 @@
 
 package com.dua3.utility.text;
 
+import org.jspecify.annotations.NonNull;
 import org.jspecify.annotations.Nullable;
 import com.dua3.utility.data.Color;
 
@@ -250,7 +251,7 @@ public final class Style implements Iterable<Map.Entry<String, Object>> {
     // -- instance fields and methods
 
     private final String name;
-    private final Map<String, Object> properties;
+    private final Map<String, @Nullable Object> properties;
 
     private Style(String name, Map<String, @Nullable Object> args) {
         this.name = name;
@@ -313,8 +314,9 @@ public String name() {
      * @param dflt     the default value
      * @return the value of the property or dflt if no value was set
      */
-    public @Nullable Object getOrDefault(String property, @Nullable Object dflt) {
-        return properties.getOrDefault(property, dflt);
+    public <T extends @Nullable Object> T getOrDefault(String property, T dflt) {
+        //noinspection unchecked
+        return (T) properties.getOrDefault(property, dflt);
     }
 
     /**
@@ -326,7 +328,7 @@ public String name() {
      * @throws ClassCastException if the property value does not match the requested type
      */
     @SuppressWarnings("unchecked")
-    public <T extends @Nullable Object> void ifPresent(String key, Consumer<T> action) throws ClassCastException {
+    public <T extends @Nullable Object> void ifPresent(String key, Consumer<@NonNull T> action) throws ClassCastException {
         T value = (T) get(key);
         if (value != null) {
             action.accept(value);
@@ -366,11 +368,12 @@ public String name() {
      */
     @SuppressWarnings("unchecked")
     public <T extends @Nullable Object> void ifPresentOrElse(String key,
-                                    T defaultValue,
+                                    @Nullable T defaultValue,
                                     Consumer<T> action) {
         Object raw = get(key);
         try {
             T value = (T) raw;
+            //noinspection DataFlowIssue
             action.accept(value != null ? value : defaultValue);
         } catch (Exception e) {
             throw new IllegalStateException("error processing attribute '" + key + "' with value: " + raw, e);
diff --git a/utility/src/main/java/com/dua3/utility/text/TagBasedConverter.java b/utility/src/main/java/com/dua3/utility/text/TagBasedConverter.java
index 58d0e0fb..a63237a1 100644
--- a/utility/src/main/java/com/dua3/utility/text/TagBasedConverter.java
+++ b/utility/src/main/java/com/dua3/utility/text/TagBasedConverter.java
@@ -1,7 +1,5 @@
 package com.dua3.utility.text;
 
-import org.jspecify.annotations.Nullable;
-
 import java.util.ArrayList;
 import java.util.List;
 
@@ -10,7 +8,7 @@
  *
  * @param <T> the conversion target type
  */
-public abstract class TagBasedConverter<T extends @Nullable Object> implements RichTextConverter<T> {
+public abstract class TagBasedConverter<T> implements RichTextConverter<T> {
 
     /**
      * Create a converter for the given argument.
diff --git a/utility/src/main/java/com/dua3/utility/xml/SimpleNamespaceContext.java b/utility/src/main/java/com/dua3/utility/xml/SimpleNamespaceContext.java
index 1b2cb552..6322edb0 100644
--- a/utility/src/main/java/com/dua3/utility/xml/SimpleNamespaceContext.java
+++ b/utility/src/main/java/com/dua3/utility/xml/SimpleNamespaceContext.java
@@ -20,7 +20,7 @@
 public class SimpleNamespaceContext implements NamespaceContext {
     private final HashMap<String, String> nsToUri;
     private final HashMap<String, List<String>> uriToNs;
-    private final String defaultPrefix;
+    private final @Nullable String defaultPrefix;
 
     /**
      * Construct new instance with mappings.
@@ -73,7 +73,7 @@ public String getNamespaceURI(String prefix) {
     }
 
     @Override
-    public String getPrefix(String namespaceURI) {
+    public @Nullable String getPrefix(String namespaceURI) {
         List<String> namespaces = uriToNs.get(namespaceURI);
         return namespaces == null || namespaces.isEmpty() ? null : namespaces.get(0);
     }
diff --git a/utility/src/main/java/com/dua3/utility/xml/XmlUtil.java b/utility/src/main/java/com/dua3/utility/xml/XmlUtil.java
index c5a99e5e..6a51032e 100644
--- a/utility/src/main/java/com/dua3/utility/xml/XmlUtil.java
+++ b/utility/src/main/java/com/dua3/utility/xml/XmlUtil.java
@@ -64,6 +64,7 @@
 import java.util.Comparator;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.Objects;
 import java.util.Spliterator;
 import java.util.function.Consumer;
 import java.util.regex.Pattern;
@@ -395,12 +396,15 @@ public String prettyPrint(String xml) {
                         writer.writeStartElement(seName.getPrefix(), seName.getLocalPart(), seName.getNamespaceURI());
                     }
                     // write namespaces and attributes in alphabetical order to obtain reproducible results
+                    //noinspection DataFlowIssue - false positive
                     StreamUtil.stream(se.getNamespaces())
                             .sorted(Comparator.comparing(Namespace::getPrefix))
                             .forEach(consume(ns -> writer.writeNamespace(ns.getPrefix(), ns.getNamespaceURI())));
                     StreamUtil.stream(se.getAttributes())
+                            .filter(Objects::nonNull)
                             .sorted(Comparator.comparing(Attribute::toString))
                             .forEach(consume(attr -> {
+                                //noinspection DataFlowIssue - false positive
                                 QName attrName = attr.getName();
                                 writer.writeAttribute(attrName.getPrefix(), attrName.getNamespaceURI(), attrName.getLocalPart(), attr.getValue());
                             }));
@@ -676,7 +680,7 @@ public boolean tryAdvance(Consumer<? super Node> action) {
         }
 
         @Override
-        public Spliterator<Node> trySplit() {
+        public @Nullable Spliterator<Node> trySplit() {
             return null;
         }