diff --git a/src/Accessor/DefaultAccessorStrategy.php b/src/Accessor/DefaultAccessorStrategy.php
index c3e45d819..450f892fe 100644
--- a/src/Accessor/DefaultAccessorStrategy.php
+++ b/src/Accessor/DefaultAccessorStrategy.php
@@ -51,7 +51,7 @@ public function __construct(?ExpressionEvaluatorInterface $evaluator = null)
     public function getValue(object $object, PropertyMetadata $metadata, SerializationContext $context)
     {
         if ($metadata instanceof StaticPropertyMetadata) {
-            return $metadata->getValue(null);
+            return $metadata->getValue();
         }
 
         if ($metadata instanceof ExpressionPropertyMetadata) {
diff --git a/src/ContextFactory/CallableContextFactory.php b/src/ContextFactory/CallableContextFactory.php
index 54e1c7ec8..a6aebe541 100644
--- a/src/ContextFactory/CallableContextFactory.php
+++ b/src/ContextFactory/CallableContextFactory.php
@@ -21,9 +21,6 @@ public function __construct(callable $callable)
         $this->callable = $callable;
     }
 
-    /**
-     * @return mixed
-     */
     protected function createContext(): Context
     {
         $callable = $this->callable;
diff --git a/src/GraphNavigator/SerializationGraphNavigator.php b/src/GraphNavigator/SerializationGraphNavigator.php
index 31ecd01ba..046934e84 100644
--- a/src/GraphNavigator/SerializationGraphNavigator.php
+++ b/src/GraphNavigator/SerializationGraphNavigator.php
@@ -29,6 +29,8 @@
 use JMS\Serializer\VisitorInterface;
 use Metadata\MetadataFactoryInterface;
 
+use function assert;
+
 /**
  * Handles traversal along the object graph.
  *
@@ -37,7 +39,7 @@
  *
  * @author Johannes M. Schmitt <schmittjoh@gmail.com>
  */
-final class SerializationGraphNavigator extends GraphNavigator implements GraphNavigatorInterface
+final class SerializationGraphNavigator extends GraphNavigator
 {
     /**
      * @var SerializationVisitorInterface
@@ -97,6 +99,8 @@ public function __construct(
 
     public function initialize(VisitorInterface $visitor, Context $context): void
     {
+        assert($context instanceof SerializationContext);
+
         parent::initialize($visitor, $context);
         $this->shouldSerializeNull = $context->shouldSerializeNull();
     }
diff --git a/src/Handler/ArrayCollectionHandler.php b/src/Handler/ArrayCollectionHandler.php
index ae839bd7f..f441720e2 100644
--- a/src/Handler/ArrayCollectionHandler.php
+++ b/src/Handler/ArrayCollectionHandler.php
@@ -75,7 +75,7 @@ public function serializeCollection(SerializationVisitorInterface $visitor, Coll
             if (null !== $exclusionStrategy && $exclusionStrategy->shouldSkipClass($context->getMetadataFactory()->getMetadataForClass(\get_class($collection)), $context)) {
                 $context->startVisiting($collection);
 
-                return $visitor->visitArray([], $type, $context);
+                return $visitor->visitArray([], $type);
             }
         }
 
diff --git a/src/Handler/StdClassHandler.php b/src/Handler/StdClassHandler.php
index 2e4686a67..983a9f1bc 100644
--- a/src/Handler/StdClassHandler.php
+++ b/src/Handler/StdClassHandler.php
@@ -40,13 +40,13 @@ public static function getSubscribingMethods()
     public function serializeStdClass(SerializationVisitorInterface $visitor, \stdClass $stdClass, array $type, SerializationContext $context)
     {
         $classMetadata = $context->getMetadataFactory()->getMetadataForClass('stdClass');
-        $visitor->startVisitingObject($classMetadata, $stdClass, ['name' => 'stdClass'], $context);
+        $visitor->startVisitingObject($classMetadata, $stdClass, ['name' => 'stdClass']);
 
         foreach ((array) $stdClass as $name => $value) {
             $metadata = new StaticPropertyMetadata('stdClass', $name, $value);
             $visitor->visitProperty($metadata, $value);
         }
 
-        return $visitor->endVisitingObject($classMetadata, $stdClass, ['name' => 'stdClass'], $context);
+        return $visitor->endVisitingObject($classMetadata, $stdClass, ['name' => 'stdClass']);
     }
 }
diff --git a/src/JsonDeserializationVisitor.php b/src/JsonDeserializationVisitor.php
index e4f8d8637..95a2ca74d 100644
--- a/src/JsonDeserializationVisitor.php
+++ b/src/JsonDeserializationVisitor.php
@@ -45,8 +45,9 @@ public function __construct(
     /**
      * {@inheritdoc}
      */
-    public function visitNull($data, array $type): void
+    public function visitNull($data, array $type)
     {
+        return null;
     }
 
     /**
diff --git a/src/Visitor/DeserializationVisitorInterface.php b/src/Visitor/DeserializationVisitorInterface.php
index 523979fd4..cf6a3f3c9 100644
--- a/src/Visitor/DeserializationVisitorInterface.php
+++ b/src/Visitor/DeserializationVisitorInterface.php
@@ -23,39 +23,31 @@ interface DeserializationVisitorInterface extends VisitorInterface
      * @param mixed $data
      * @param array $type
      *
-     * @return mixed
+     * @return null
      */
-    public function visitNull($data, array $type): void;
+    public function visitNull($data, array $type);
 
     /**
      * @param mixed $data
      * @param array $type
-     *
-     * @return mixed
      */
     public function visitString($data, array $type): string;
 
     /**
      * @param mixed $data
      * @param array $type
-     *
-     * @return mixed
      */
     public function visitBoolean($data, array $type): bool;
 
     /**
      * @param mixed $data
      * @param array $type
-     *
-     * @return mixed
      */
     public function visitDouble($data, array $type): float;
 
     /**
      * @param mixed $data
      * @param array $type
-     *
-     * @return mixed
      */
     public function visitInteger($data, array $type): int;
 
@@ -70,7 +62,7 @@ public function visitDiscriminatorMapProperty($data, ClassMetadata $metadata): s
      * @param mixed $data
      * @param array $type
      *
-     * @return mixed
+     * @return array<mixed>
      */
     public function visitArray($data, array $type): array;
 
diff --git a/src/XmlDeserializationVisitor.php b/src/XmlDeserializationVisitor.php
index 28861997f..a14f0835e 100644
--- a/src/XmlDeserializationVisitor.php
+++ b/src/XmlDeserializationVisitor.php
@@ -118,8 +118,9 @@ private function emptyStringToSpaceCharacter($data): string
     /**
      * {@inheritdoc}
      */
-    public function visitNull($data, array $type): void
+    public function visitNull($data, array $type)
     {
+        return null;
     }
 
     /**
diff --git a/tests/Handler/DateHandlerTest.php b/tests/Handler/DateHandlerTest.php
index 5b099557d..258a88e94 100644
--- a/tests/Handler/DateHandlerTest.php
+++ b/tests/Handler/DateHandlerTest.php
@@ -64,17 +64,15 @@ public function testSerializeDate(array $params)
      */
     public function testDeserializeDateInterval($dateInterval, $expected)
     {
-        $context = $this->getMockBuilder(SerializationContext::class)->getMock();
-
         $visitor = $this->getMockBuilder(DeserializationVisitorInterface::class)->getMock();
         $visitor->method('visitString')->with('2017-06-18');
 
-        $deserialized = $this->handler->deserializeDateIntervalFromJson($visitor, $dateInterval, [], $context);
+        $deserialized = $this->handler->deserializeDateIntervalFromJson($visitor, $dateInterval, []);
         if (isset($deserialized->f)) {
-            $this->assertEquals($expected['f'], $deserialized->f);
+            self::assertEquals($expected['f'], $deserialized->f);
         }
 
-        $this->assertEquals($expected['s'], $deserialized->s);
+        self::assertEquals($expected['s'], $deserialized->s);
     }
 
     public function getDeserializeDateInterval()
diff --git a/tests/Handler/FormErrorHandlerTest.php b/tests/Handler/FormErrorHandlerTest.php
index 47cdfbe68..c92539cc7 100644
--- a/tests/Handler/FormErrorHandlerTest.php
+++ b/tests/Handler/FormErrorHandlerTest.php
@@ -4,10 +4,8 @@
 
 namespace JMS\Serializer\Tests\Handler;
 
-use JMS\Serializer\GraphNavigatorInterface;
 use JMS\Serializer\Handler\FormErrorHandler;
 use JMS\Serializer\JsonSerializationVisitor;
-use JMS\Serializer\SerializationContext;
 use JMS\Serializer\Visitor\Factory\JsonSerializationVisitorFactory;
 use PHPUnit\Framework\MockObject\MockObject;
 use PHPUnit\Framework\TestCase;
@@ -53,11 +51,9 @@ class FormErrorHandlerTest extends TestCase
     protected function setUp(): void
     {
         $this->handler = new FormErrorHandler(new Translator('en'));
-        $navigator = $this->getMockBuilder(GraphNavigatorInterface::class)->getMock();
-        $context = SerializationContext::create();
-        $this->visitor = (new JsonSerializationVisitorFactory())->getVisitor($navigator, $context);
+        $this->visitor = (new JsonSerializationVisitorFactory())->getVisitor();
         $this->dispatcher = new EventDispatcher();
-        $this->factory = $this->getMockBuilder('Symfony\Component\Form\FormFactoryInterface')->getMock();
+        $this->factory = $this->getMockBuilder(FormFactoryInterface::class)->getMock();
     }
 
     protected function tearDown(): void
diff --git a/tests/Serializer/EventDispatcher/Subscriber/SymfonyValidatorValidatorSubscriberTest.php b/tests/Serializer/EventDispatcher/Subscriber/SymfonyValidatorValidatorSubscriberTest.php
index 2e03ebb02..d318a421b 100644
--- a/tests/Serializer/EventDispatcher/Subscriber/SymfonyValidatorValidatorSubscriberTest.php
+++ b/tests/Serializer/EventDispatcher/Subscriber/SymfonyValidatorValidatorSubscriberTest.php
@@ -7,43 +7,45 @@
 use JMS\Serializer\DeserializationContext;
 use JMS\Serializer\EventDispatcher\EventDispatcher;
 use JMS\Serializer\EventDispatcher\ObjectEvent;
-use JMS\Serializer\EventDispatcher\Subscriber\SymfonyValidatorSubscriber;
 use JMS\Serializer\EventDispatcher\Subscriber\SymfonyValidatorValidatorSubscriber;
 use JMS\Serializer\Exception\ValidationFailedException;
 use JMS\Serializer\SerializerBuilder;
+use JMS\Serializer\Tests\Fixtures\AuthorList;
 use PHPUnit\Framework\TestCase;
+use stdClass;
 use Symfony\Component\Validator\ConstraintViolation;
 use Symfony\Component\Validator\ConstraintViolationList;
+use Symfony\Component\Validator\Validator\ValidatorInterface;
 
 class SymfonyValidatorValidatorSubscriberTest extends TestCase
 {
     private $validator;
 
-    /** @var SymfonyValidatorSubscriber */
+    /** @var SymfonyValidatorValidatorSubscriber */
     private $subscriber;
 
-    public function testValidate()
+    public function testValidate(): void
     {
-        $obj = new \stdClass();
+        $obj = new stdClass();
 
-        $this->validator->expects($this->once())
+        $this->validator->expects(self::once())
             ->method('validate')
             ->with($obj, null, ['foo'])
-            ->will($this->returnValue(new ConstraintViolationList()));
+            ->willReturn(new ConstraintViolationList());
 
         $context = DeserializationContext::create()->setAttribute('validation_groups', ['foo']);
 
         $this->subscriber->onPostDeserialize(new ObjectEvent($context, $obj, []));
     }
 
-    public function testValidateThrowsExceptionWhenListIsNotEmpty()
+    public function testValidateThrowsExceptionWhenListIsNotEmpty(): void
     {
-        $obj = new \stdClass();
+        $obj = new stdClass();
 
-        $this->validator->expects($this->once())
+        $this->validator->expects(self::once())
             ->method('validate')
             ->with($obj, null, ['foo'])
-            ->will($this->returnValue(new ConstraintViolationList([new ConstraintViolation('foo', 'foo', [], 'a', 'b', 'c')])));
+            ->willReturn(new ConstraintViolationList([new ConstraintViolation('foo', 'foo', [], 'a', 'b', 'c')]));
 
         $context = DeserializationContext::create()->setAttribute('validation_groups', ['foo']);
 
@@ -53,20 +55,20 @@ public function testValidateThrowsExceptionWhenListIsNotEmpty()
         $this->subscriber->onPostDeserialize(new ObjectEvent($context, $obj, []));
     }
 
-    public function testValidatorIsNotCalledWhenNoGroupsAreSet()
+    public function testValidatorIsNotCalledWhenNoGroupsAreSet(): void
     {
-        $this->validator->expects($this->never())
+        $this->validator->expects(self::never())
             ->method('validate');
 
-        $this->subscriber->onPostDeserialize(new ObjectEvent(DeserializationContext::create(), new \stdClass(), []));
+        $this->subscriber->onPostDeserialize(new ObjectEvent(DeserializationContext::create(), new stdClass(), []));
     }
 
-    public function testValidationIsOnlyPerformedOnRootObject()
+    public function testValidationIsOnlyPerformedOnRootObject(): void
     {
-        $this->validator->expects($this->once())
+        $this->validator->expects(self::once())
             ->method('validate')
-            ->with($this->isInstanceOf('JMS\Serializer\Tests\Fixtures\AuthorList'), null, ['Foo'])
-            ->will($this->returnValue(new ConstraintViolationList()));
+            ->with(self::isInstanceOf(AuthorList::class), null, ['Foo'])
+            ->willReturn(new ConstraintViolationList());
 
         $subscriber = $this->subscriber;
         $list = SerializerBuilder::create()
@@ -76,7 +78,7 @@ public function testValidationIsOnlyPerformedOnRootObject()
             ->build()
             ->deserialize(
                 '{"authors":[{"full_name":"foo"},{"full_name":"bar"}]}',
-                'JMS\Serializer\Tests\Fixtures\AuthorList',
+                AuthorList::class,
                 'json',
                 DeserializationContext::create()->setAttribute('validation_groups', ['Foo'])
             );
@@ -86,7 +88,7 @@ public function testValidationIsOnlyPerformedOnRootObject()
 
     protected function setUp(): void
     {
-        $this->validator = $this->getMockBuilder('Symfony\Component\Validator\Validator\ValidatorInterface')->getMock();
+        $this->validator = $this->getMockBuilder(ValidatorInterface::class)->getMock();
         $this->subscriber = new SymfonyValidatorValidatorSubscriber($this->validator);
     }
 }