Interaction.py: getGuard allow to return none if necessary.

product/ERP5Workflow/Document/Interaction.py

@@ -93,18 +93,24 @@ class Interaction(IdAsReferenceMixin('interaction_', "prefix"), XMLObject):
 
   def getGuardSummary(self):
     res = None
-    if self.guard is not None:
+    if self.getGuard() is not None:
       res = self.guard.getSummary()
     return res
 
   def getGuard(self):
-    self.generateGuard()
+    if self.getRoleList() is None and\
+        self.getPermissionList() is None and\
+        self.getGroupList() is None and\
+        self.getExpression() is None and\
+        self.guard is None:
+      return None
+    else:
+      self.generateGuard()
     return self.guard
 
   def generateGuard(self):
     if self.guard is None:
-      self.guard = Guard()
-
+      self.guard = Guard().__of__(self)
     if self.getRoleList() is not None:
       self.guard.roles = self.getRoleList()
     if self.getPermissionList() is not None: