diff --git a/components/serializer.rst b/components/serializer.rst
index 0e8af7814f3..43ed69f3307 100644
--- a/components/serializer.rst
+++ b/components/serializer.rst
@@ -1500,7 +1500,7 @@ having unique identifiers::
 
     $encoder = new JsonEncoder();
     $defaultContext = [
-        AbstractNormalizer::CIRCULAR_REFERENCE_HANDLER => function (object $object, string $format, array $context): string {
+        AbstractNormalizer::CIRCULAR_REFERENCE_HANDLER => function (object $object, ?string $format, array $context): string {
             return $object->getName();
         },
     ];