Add Reference property. Because BusinessPath has already used the references.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@34412 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/Document/BusinessPath.py

@@ -82,6 +82,7 @@ class BusinessPath(Path, Predicate):
                     , PropertySheet.Chain
                     , PropertySheet.SortIndex
                     , PropertySheet.BusinessPath
+                    , PropertySheet.Reference
                     )
 
   # Declarative interfaces