Workflow.py: when workflow managed role list is not defined, return an empty...

Workflow.py: when workflow managed role list is not defined, return an empty tuple to variable_match instead of None.

product/ERP5Workflow/Document/Workflow.py

@@ -403,7 +403,11 @@ class Workflow(IdAsReferenceMixin("", "prefix"), XMLObject):
         elif (not check_guard) or \
             Guard_checkWithoutRoles(guard, security_manager, self, portal):
           is_permitted_worklist = 1
-          variable_match[SECURITY_PARAMETER_ID] = worklist_definition.getRoleList()
+          workflow_role_list = worklist_definition.getRoleList()
+          if workflow_role_list is not None:
+            variable_match[SECURITY_PARAMETER_ID] = workflow_role_list
+          else:
+            variable_match[SECURITY_PARAMETER_ID] = ()
 
         if is_permitted_worklist:
           fmt_data = TemplateDict()