Variable.py: make variable guard functional.

product/ERP5Workflow/Document/Variable.py

@@ -80,14 +80,14 @@ class Variable(IdAsReferenceMixin("variable_", "prefix"), XMLObject):
                         groups=self.getGroupList(),
                         expr=self.getExpression())
 
-        if self.info_guard.roles != self.getRoleList():
+        if self.getRoleList() is not None:
           self.info_guard.roles = self.getRoleList()
-        elif self.info_guard.permissions != self.getPermissionList():
+        if self.getPermissionList() is not None:
           self.info_guard.permissions = self.getPermissionList()
-        elif self.info_guard.groups != self.getGroupList():
+        if self.getGroupList() is not None:
           self.info_guard.groups = self.getGroupList()
-        elif self.info_guard.expr != self.getExpression():
-          self.info_guard.expr = self.getExpression()
+        if self.getExpression() is not None:
+          self.info_guard.expr = Expression(self.getExpression())
 
     def getInfoGuard(self):
         if self.info_guard is not None: