AttributeError: 'NoneType' object has no attribute 'transport'

[4ZM]

After running for a few days, the server gets an exception. Not sure what triggered it.

return context.call({ILogContext: newCtx}, func, *args, **kw)

File "/usr/lib/python2.7/site-packages/twisted/python/context.py", line 118, in callWithContext
return self.currentContext().callWithContext(ctx, func, _args, *_kw)
File "/usr/lib/python2.7/site-packages/twisted/python/context.py", line 81, in callWithContext
return func(_args,__kw)
--- ---
File "/usr/lib/python2.7/site-packages/twisted/internet/epollreactor.py", line 217, in _doReadOrWrite
why = selectable.doRead()
File "/usr/lib/python2.7/site-packages/twisted/internet/tcp.py", line 460, in doRead
rval = self.protocol.dataReceived(data)
File "/usr/lib/python2.7/site-packages/twisted/protocols/basic.py", line 572, in dataReceived
return self.rawDataReceived(data)
File "/usr/lib/python2.7/site-packages/convergence/ConnectChannel.py", line 35, in rawDataReceived
self.proxyConnection.transport.write(data)
exceptions.AttributeError: 'NoneType' object has no attribute 'transport'
Unhandled Error
Traceback (most recent call last):
File "/usr/lib/python2.7/site-packages/twisted/python/log.py", line 84, in callWithLogger
return callWithContext({"system": lp}, func, *args, *_kw)
File "/usr/lib/python2.7/site-packages/twisted/python/log.py", line 69, in callWithContext
return context.call({ILogContext: newCtx}, func, _args, *_kw)
File "/usr/lib/python2.7/site-packages/twisted/python/context.py", line 118, in callWithContext
return self.currentContext().callWithContext(ctx, func, _args, *_kw)
File "/usr/lib/python2.7/site-packages/twisted/python/context.py", line 81, in callWithContext
return func(args,*kw)
--- ---
File "/usr/lib/python2.7/site-packages/twisted/internet/epollreactor.py", line 217, in _doReadOrWrite
why = selectable.doRead()
File "/usr/lib/python2.7/site-packages/twisted/internet/tcp.py", line 460, in doRead
rval = self.protocol.dataReceived(data)
File "/usr/lib/python2.7/site-packages/twisted/protocols/basic.py", line 572, in dataReceived
return self.rawDataReceived(data)
File "/usr/lib/python2.7/site-packages/convergence/ConnectChannel.py", line 35, in rawDataReceived
self.proxyConnection.transport.write(data)
exceptions.AttributeError: 'NoneType' object has no attribute 'transport'