Unhandled error: "'NoneType' object has no attribute 'writeHeaders'"

[tsnork]

2020-02-04T13:09:03+0100 [XmlStream,client] Unhandled Error Traceback (most recent call last): File "c:\python27amd64\lib\site-packages\punjab\session.py", line 117, in doCallback self.deferred.callback(data) File "c:\python27amd64\lib\site-packages\twisted\internet\defer.py", line 460, in callback self._startRunCallbacks(result) File "c:\python27amd64\lib\site-packages\twisted\internet\defer.py", line 568, in _startRunCallbacks self._runCallbacks() File "c:\python27amd64\lib\site-packages\twisted\internet\defer.py", line 654, in _runCallbacks current.result = callback(current.result, *args, **kw) --- <exception caught here> --- File "c:\python27amd64\lib\site-packages\punjab\httpb.py", line 493, in return_error self.send_http_error(error.conditions[str(e.value)]['code'], exceptions.KeyError: "'NoneType' object has no attribute 'writeHeaders'"