Allow normalization on classes implementing \Traversable interface

src/Serializer/AbstractItemNormalizer.php

@@ -90,7 +90,7 @@ public function __construct(PropertyNameCollectionFactoryInterface $propertyName
      */
     public function supportsNormalization($data, $format = null)
     {
-        if (!\is_object($data) || $data instanceof \Traversable) {
+        if (!\is_object($data)) {
             return false;
         }