Does not return working copy information when serializing Portal in

Plone 5.2

src/plone/restapi/serializer/dxcontent.py

@@ -5,6 +5,7 @@
 from plone.dexterity.interfaces import IDexterityContainer
 from plone.dexterity.interfaces import IDexterityContent
 from plone.dexterity.utils import iterSchemata
+from plone.restapi import HAS_PLONE_6
 from plone.restapi.batching import HypermediaBatch
 from plone.restapi.deserializer import boolean_value
 from plone.restapi.interfaces import IFieldSerializer
@@ -42,7 +43,7 @@
 
 
 def update_with_working_copy_info(context, result):
-    if WorkingCopyInfo is not None:
+    if WorkingCopyInfo is not None and HAS_PLONE_6:
         baseline, working_copy = WorkingCopyInfo(context).get_working_copy_info()
         result.update({"working_copy": working_copy, "working_copy_of": baseline})