Traceback (most recent call last): File "/usr/local/lib/python2.7/dist-packages/tornado/web.py", line 1467, in _execute result = method(*self.path_args, **self.path_kwargs) File "/root/xyzgate/app/file/MarkdownHandlers.py", line 67, in get author = db.user.find_one({"_id" : ObjectId(article["owner"])}) TypeError: 'NoneType' object has no attribute '__getitem__'