If template_catalog_method_id is None, assign result to an empty tuple.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@749 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/Document/BusinessTemplate.py

@@ -361,6 +361,7 @@ Une ligne tarifaire."""
       ordered list
       """
       result = getattr(self,'template_catalog_method_id',())
+      if result is None: result = ()
       if result != ():
         result = list(result)
         result.sort()