diff --git a/Normalizer/CustomNormalizer.php b/Normalizer/CustomNormalizer.php
index 44ad1771b..ebe2f0f69 100644
--- a/Normalizer/CustomNormalizer.php
+++ b/Normalizer/CustomNormalizer.php
@@ -44,8 +44,8 @@ public function denormalize($data, string $type, string $format = null, array $c
     /**
      * Checks if the given class implements the NormalizableInterface.
      *
-     * @param mixed  $data   Data to normalize
-     * @param string $format The format being (de-)serialized from or into
+     * @param mixed       $data   Data to normalize
+     * @param string|null $format The format being (de-)serialized from or into
      *
      * @return bool
      */
@@ -57,9 +57,9 @@ public function supportsNormalization($data, string $format = null)
     /**
      * Checks if the given class implements the DenormalizableInterface.
      *
-     * @param mixed  $data   Data to denormalize from
-     * @param string $type   The class to which the data should be denormalized
-     * @param string $format The format being deserialized from
+     * @param mixed       $data   Data to denormalize from
+     * @param string      $type   The class to which the data should be denormalized
+     * @param string|null $format The format being deserialized from
      *
      * @return bool
      */
diff --git a/Normalizer/DenormalizerInterface.php b/Normalizer/DenormalizerInterface.php
index 5b7d7f228..e3f7113b1 100644
--- a/Normalizer/DenormalizerInterface.php
+++ b/Normalizer/DenormalizerInterface.php
@@ -29,10 +29,10 @@ interface DenormalizerInterface
     /**
      * Denormalizes data back into an object of the given class.
      *
-     * @param mixed  $data    Data to restore
-     * @param string $type    The expected class to instantiate
-     * @param string $format  Format the given data was extracted from
-     * @param array  $context Options available to the denormalizer
+     * @param mixed       $data    Data to restore
+     * @param string      $type    The expected class to instantiate
+     * @param string|null $format  Format the given data was extracted from
+     * @param array       $context Options available to the denormalizer
      *
      * @return mixed
      *
@@ -49,9 +49,9 @@ public function denormalize($data, string $type, string $format = null, array $c
     /**
      * Checks whether the given class is supported for denormalization by this normalizer.
      *
-     * @param mixed  $data   Data to denormalize from
-     * @param string $type   The class to which the data should be denormalized
-     * @param string $format The format being deserialized from
+     * @param mixed       $data   Data to denormalize from
+     * @param string      $type   The class to which the data should be denormalized
+     * @param string|null $format The format being deserialized from
      *
      * @return bool
      */
diff --git a/Normalizer/NormalizerInterface.php b/Normalizer/NormalizerInterface.php
index 653f94954..b282f1dd6 100644
--- a/Normalizer/NormalizerInterface.php
+++ b/Normalizer/NormalizerInterface.php
@@ -24,9 +24,9 @@ interface NormalizerInterface
     /**
      * Normalizes an object into a set of arrays/scalars.
      *
-     * @param mixed  $object  Object to normalize
-     * @param string $format  Format the normalization result will be encoded as
-     * @param array  $context Context options for the normalizer
+     * @param mixed       $object  Object to normalize
+     * @param string|null $format  Format the normalization result will be encoded as
+     * @param array       $context Context options for the normalizer
      *
      * @return array|string|int|float|bool|\ArrayObject|null \ArrayObject is used to make sure an empty object is encoded as an object not an array
      *
@@ -41,8 +41,8 @@ public function normalize($object, string $format = null, array $context = []);
     /**
      * Checks whether the given class is supported for normalization by this normalizer.
      *
-     * @param mixed  $data   Data to normalize
-     * @param string $format The format being (de-)serialized from or into
+     * @param mixed       $data   Data to normalize
+     * @param string|null $format The format being (de-)serialized from or into
      *
      * @return bool
      */
diff --git a/Serializer.php b/Serializer.php
index d5fda3b8c..c0a49a808 100644
--- a/Serializer.php
+++ b/Serializer.php
@@ -257,9 +257,9 @@ public function supportsDenormalization($data, string $type, string $format = nu
     /**
      * Returns a matching normalizer.
      *
-     * @param mixed  $data    Data to get the serializer for
-     * @param string $format  Format name, present to give the option to normalizers to act differently based on formats
-     * @param array  $context Options available to the normalizer
+     * @param mixed       $data    Data to get the serializer for
+     * @param string|null $format  Format name, present to give the option to normalizers to act differently based on formats
+     * @param array       $context Options available to the normalizer
      */
     private function getNormalizer($data, ?string $format, array $context): ?NormalizerInterface
     {
@@ -295,10 +295,10 @@ private function getNormalizer($data, ?string $format, array $context): ?Normali
     /**
      * Returns a matching denormalizer.
      *
-     * @param mixed  $data    Data to restore
-     * @param string $class   The expected class to instantiate
-     * @param string $format  Format name, present to give the option to normalizers to act differently based on formats
-     * @param array  $context Options available to the denormalizer
+     * @param mixed       $data    Data to restore
+     * @param string      $class   The expected class to instantiate
+     * @param string|null $format  Format name, present to give the option to normalizers to act differently based on formats
+     * @param array       $context Options available to the denormalizer
      */
     private function getDenormalizer($data, string $class, ?string $format, array $context): ?DenormalizerInterface
     {