[Zope] External Method 3

Ok, now I found the error. The error must be in the while loop, where we say 'iterate until the obj = None'. However 'None' is never reached... (I guess). The following code works, but I this isn't at all a good solution. Can someone tell me how I can safely test that the current object is the first object in the object database. In other laguages you can test this with 'nil'. How can I test this within Zope? Please, tell me! def GetParentNames(self): result=[] obj=self while obj.title != 'Zope': obj=obj.aq_parent if obj.meta_type=='KBItem': result.append(obj.Title) return result Thanks in advance, Tom.