diff --git a/framework/core/src/Api/Serializer/AbstractSerializer.php b/framework/core/src/Api/Serializer/AbstractSerializer.php
index 78d3ae42b..3f7b245e2 100644
--- a/framework/core/src/Api/Serializer/AbstractSerializer.php
+++ b/framework/core/src/Api/Serializer/AbstractSerializer.php
@@ -186,6 +186,7 @@ abstract class AbstractSerializer extends BaseAbstractSerializer
 
     /**
      * @param mixed $model
+     * @param string $relation
      * @return mixed
      */
     protected function getRelationshipData($model, $relation)