diff --git a/src/Lemon/DataMapper/DataMapper.php b/src/Lemon/DataMapper/DataMapper.php
index a44b448..64f8b8e 100644
--- a/src/Lemon/DataMapper/DataMapper.php
+++ b/src/Lemon/DataMapper/DataMapper.php
@@ -38,18 +38,18 @@ public static function typeCheck(mixed $value, ReflectionType $type): Maybe
     {
         $type_name = trim((string) $type, '?');
         if (class_exists($type_name)) {
-            if ($type->allowsNull() && $value === null) {
+            if ($type->allowsNull() && null === $value) {
                 return Maybe::just(null);
             }
 
             if (!is_array($value)) {
                 return Maybe::nothing();
-            } 
+            }
 
             return ($v = static::mapTo($value, $type_name)) === null ? Maybe::nothing() : Maybe::just($v);
         }
 
-        if (!$type->allowsNull() && $value === null) {
+        if (!$type->allowsNull() && null === $value) {
             return Maybe::nothing();
         }
 
diff --git a/tests/Http/RequestTest.php b/tests/Http/RequestTest.php
index ddf1ba2..589844f 100644
--- a/tests/Http/RequestTest.php
+++ b/tests/Http/RequestTest.php
@@ -156,15 +156,17 @@ public function testValidationSuccess()
     public function testMustBe(): void
     {
         $r = new Request('/', '', 'GET', ['Content-Type' => 'application/json'], '{"foo":10}', [], [], '');
-        $f = new \Fiber(function(Request $r) {
+        $f = new \Fiber(function (Request $r) {
             $r->mustBe('application/parek', 'foo');
+
             return 'bar';
         });
 
         $this->assertSame('foo', $f->start($r));
 
-        $f = new \Fiber(function(Request $r) {
+        $f = new \Fiber(function (Request $r) {
             $r->mustBe('application/json', 'foo');
+
             return 'bar';
         });