diff --git a/src/Symfony/Component/Serializer/NameConverter/MetadataAwareNameConverter.php b/src/Symfony/Component/Serializer/NameConverter/MetadataAwareNameConverter.php
index a6934f54b8..e863e013e7 100644
--- a/src/Symfony/Component/Serializer/NameConverter/MetadataAwareNameConverter.php
+++ b/src/Symfony/Component/Serializer/NameConverter/MetadataAwareNameConverter.php
@@ -69,7 +69,7 @@ final class MetadataAwareNameConverter implements AdvancedNameConverterInterface
         return self::$denormalizeCache[$class][$propertyName] ?? $this->denormalizeFallback($propertyName, $class, $format, $context);
     }
 
-    private function getCacheValueForNormalization(string $propertyName, string $class): ?string
+    private function getCacheValueForNormalization($propertyName, string $class)
     {
         if (!$this->metadataFactory->hasMetadataFor($class)) {
             return null;
@@ -83,12 +83,12 @@ final class MetadataAwareNameConverter implements AdvancedNameConverterInterface
         return $attributesMetadata[$propertyName]->getSerializedName() ?? null;
     }
 
-    private function normalizeFallback(string $propertyName, string $class = null, string $format = null, array $context = []): string
+    private function normalizeFallback($propertyName, string $class = null, string $format = null, array $context = [])
     {
         return $this->fallbackNameConverter ? $this->fallbackNameConverter->normalize($propertyName, $class, $format, $context) : $propertyName;
     }
 
-    private function getCacheValueForDenormalization(string $propertyName, string $class): ?string
+    private function getCacheValueForDenormalization($propertyName, string $class)
     {
         if (!isset(self::$attributesMetadataCache[$class])) {
             self::$attributesMetadataCache[$class] = $this->getCacheValueForAttributesMetadata($class);
@@ -97,7 +97,7 @@ final class MetadataAwareNameConverter implements AdvancedNameConverterInterface
         return self::$attributesMetadataCache[$class][$propertyName] ?? null;
     }
 
-    private function denormalizeFallback(string $propertyName, string $class = null, string $format = null, array $context = []): string
+    private function denormalizeFallback($propertyName, string $class = null, string $format = null, array $context = [])
     {
         return $this->fallbackNameConverter ? $this->fallbackNameConverter->denormalize($propertyName, $class, $format, $context) : $propertyName;
     }
diff --git a/src/Symfony/Component/Serializer/Tests/NameConverter/MetadataAwareNameConverterTest.php b/src/Symfony/Component/Serializer/Tests/NameConverter/MetadataAwareNameConverterTest.php
index f4c5c5b305..7e2552ea8a 100644
--- a/src/Symfony/Component/Serializer/Tests/NameConverter/MetadataAwareNameConverterTest.php
+++ b/src/Symfony/Component/Serializer/Tests/NameConverter/MetadataAwareNameConverterTest.php
@@ -102,6 +102,7 @@ final class MetadataAwareNameConverterTest extends TestCase
             ['foo', 'baz'],
             ['bar', 'qux'],
             ['quux', 'quux'],
+            [0, 0],
         ];
     }
 
@@ -111,6 +112,7 @@ final class MetadataAwareNameConverterTest extends TestCase
             ['foo', 'baz'],
             ['bar', 'qux'],
             ['quux', 'QUUX'],
+            [0, 0],
         ];
     }
 }