Traceback (most recent call last):


 "/usr/lib/python3.6/site-packages/aiohttp/web_protocol.py", line 405, in start

await resp.prepare(request)


 "/usr/lib/python3.6/site-packages/aiohttp/web_response.py", line 300, in prepare

return await self._start(request)


 "/usr/lib/python3.6/site-packages/aiohttp/web_response.py", line 605, in _start

return await super()._start(request)


 "/usr/lib/python3.6/site-packages/aiohttp/web_response.py", line 367, in _start

await writer.write_headers(status_line, headers)


 "/usr/lib/python3.6/site-packages/aiohttp/http_writer.py", line 100, in write_headers

buf = _serialize_headers(status_line, headers)


 "aiohttp/_http_writer.pyx", line 138, in aiohttp._http_writer._serialize_headers


 "aiohttp/_http_writer.pyx", line 110, in aiohttp._http_writer.to_str
TypeError: Cannot serialize non-str key None


Traceback (most recent call last):

 "jupyterhub/jupyterhub/app.py", line 1293, in launch_instance_async
yield self.initialize(argv)

 "/usr/lib64/python3.5/types.py", line 199, in __next__
return next(self.__wrapped)

 "jupyterhub/jupyterhub/app.py", line 1085, in initialize
self.load_config_file(self.config_file)

 "<decorator-gen-5>", line 2, in load_config_file

 "traitlets/config/application.py", line 74, in catch_config_error
return method(app, *args, **kwargs)

 "traitlets/config/application.py", line 565, in load_config_file
self.update_config(config)

 "traitlets/config/configurable.py", line 192, in update_config
self._load_config(config)

 "traitlets/config/configurable.py", line 169, in _load_config
warn(msg)

 "/usr/lib64/python3.5/contextlib.py", line 66, in __exit__
next(self.gen)

 "traitlets/traitlets.py", line 1085, in hold_trait_notifications
self.notify_change(change)

 "traitlets/traitlets.py", line 1127, in notify_change
c(change)
TypeError: _hub_prefix_changed() missing 2 required positional arguments: 'old' and 'new'