minor #9864 Add all serialized class properties (liviubalan)

This PR was submitted for the 2.7 branch but it was merged into the 2.8 branch instead (closes #9864).

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Add all serialized class properties

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854cb23 Add all serialized class properties

Author: javiereguiluz

components/serializer.rst

@@ -135,7 +135,7 @@ use the Serializer service created before::
 
     $jsonContent = $serializer->serialize($person, 'json');
 
-    // $jsonContent contains {"name":"foo","age":99,"sportsperson":false}
+    // $jsonContent contains {"name":"foo","age":99,"sportsperson":false,"createdAt":null}
 
     echo $jsonContent; // or return it in a Response