[Serializer] Fix AbstractObjectNormalizer TypeError on denormalization

Author: JustDylan23

src/Symfony/Component/Serializer/Normalizer/AbstractNormalizer.php

@@ -296,7 +296,7 @@ protected function isAllowedAttribute(object|string $classOrObject, string $attr
      * Normalizes the given data to an array. It's particularly useful during
      * the denormalization process.
      */
-    protected function prepareForDenormalization(object|array|null $data): array
+    protected function prepareForDenormalization(mixed $data): array
     {
         return (array) $data;
     }

src/Symfony/Component/Serializer/Tests/Normalizer/AbstractObjectNormalizerTest.php

@@ -14,6 +14,7 @@
 use Doctrine\Common\Annotations\AnnotationReader;
 use PHPUnit\Framework\TestCase;
 use Symfony\Component\PropertyInfo\Extractor\PhpDocExtractor;
+use Symfony\Component\PropertyInfo\Extractor\ReflectionExtractor;
 use Symfony\Component\PropertyInfo\Type;
 use Symfony\Component\Serializer\Exception\ExtraAttributesException;
 use Symfony\Component\Serializer\Exception\InvalidArgumentException;
@@ -387,6 +388,17 @@ public function testNormalizeEmptyObject()
         $normalizedData = $normalizer->normalize(new EmptyDummy(), 'any', ['preserve_empty_objects' => true]);
         $this->assertEquals(new \ArrayObject(), $normalizedData);
     }
+
+    public function testDenormalizeRecursiveWithObjectAttributeWithStringValue()
+    {
+        $extractor = new ReflectionExtractor();
+        $normalizer = new ObjectNormalizer(null, null, null, $extractor);
+        $serializer = new Serializer([$normalizer]);
+
+        $obj = $serializer->denormalize(['inner' => 'foo'], ObjectOuter::class);
+
+        $this->assertInstanceOf(ObjectInner::class, $obj->getInner());
+    }
 }
 
 class AbstractObjectNormalizerDummy extends AbstractObjectNormalizer