cover the case where reference = ''

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@34400 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/Document/WebSection.py

@@ -118,7 +118,7 @@ class WebSection(Domain, PermanentURLMixIn):
         document = PermanentURLMixIn.__bobo_traverse__(self, request, name)
       except NotFound:
         not_found_page_ref = self.getLayoutProperty('layout_not_found_page_reference')
-        if not_found_page_ref is not None:
+        if not_found_page_ref:
           document = PermanentURLMixIn.getDocumentValue(self, name=not_found_page_ref)
         if document is None:
           # if no document found, fallback on default page template