if reference is None, we want to return it

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@27299 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/Document/TradeCondition.py

@@ -152,7 +152,7 @@ class TradeCondition(Path, Transformation):
         for trade_model_line in specialise.contentValues(
             portal_type=self.model_line_portal_type_list):
           reference = trade_model_line.getReference()
-          if reference not in reference_list:
+          if reference not in reference_list or reference is None:
             trade_model_line_composed_list.append(trade_model_line)
             reference_list.append(reference)