NPE during the release of a lock (#599)

src/main/java/org/jenkins/plugins/lockableresources/actions/LockedResourcesBuildAction.java

@@ -77,7 +77,12 @@ public static void updateAction(Run<?, ?> build, List<String> resourceNames) {
 
         for (String name : resourceNames) {
             LockableResource r = LockableResourcesManager.get().fromName(name);
-            action.add(new ResourcePOJO(r));
+            if (r != null) {
+                action.add(new ResourcePOJO(r));
+            } else {
+                // probably a ephemeral resource has been deleted
+                action.add(new ResourcePOJO(name, ""));
+            }
         }
     }
 
@@ -101,7 +106,11 @@ private void add(ResourcePOJO r) {
     @Restricted(NoExternalUse.class)
     public static LockedResourcesBuildAction fromResources(Collection<LockableResource> resources) {
         List<ResourcePOJO> resPojos = new ArrayList<>();
-        for (LockableResource r : resources) resPojos.add(new ResourcePOJO(r));
+        for (LockableResource r : resources) {
+            if (r != null) {
+                resPojos.add(new ResourcePOJO(r));
+            }
+        }
         return new LockedResourcesBuildAction(resPojos);
     }