self.channel.writeHeaders(version, code, reason, headers)\nbuiltins.AttributeError: \'NoneType\' object has no attribute \'writeHeaders\'\

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Hi,
  I have a twisted server. And I have been seeing this annoying issue.
Normally. when i develop and test it out. everything is fine..
But then I try to loadtest is via https://locust.io/

Again, everything is fine.. until I "stop" the test.
Then, I see this
'Traceback (most recent call last):\n  File
"/usr/local/Cellar/python/3.7.1/Frameworks/Python.framework/Versions/3.7/lib/python3.7/asyncio/events.py",
line 88, in _run\n    self._context.run(self._callback, *self._args)\n
 File "/usr/local/lib/python3.7/site-packages/twisted/internet/defer.py",
line 827, in adapt\n    adapt.actual.callback(extracted)\n  File
"/usr/local/lib/python3.7/site-packages/twisted/internet/defer.py", line
460, in callback\n    self._startRunCallbacks(result)\n  File
"/usr/local/lib/python3.7/site-packages/twisted/internet/defer.py", line
568, in _startRunCallbacks\n    self._runCallbacks()\n--- <exception caught
here> ---\n  File
"/usr/local/lib/python3.7/site-packages/twisted/internet/defer.py", line
654, in _runCallbacks\n    current.result = callback(current.result, *args,
**kw)\n  File
....
 File "/usr/local/lib/python3.7/site-packages/twisted/web/server.py", line
238, in write\n    http.Request.write(self, data)\n  File
"/usr/local/lib/python3.7/site-packages/twisted/web/http.py", line 1118, in
write\n    self.channel.writeHeaders(version, code, reason,
headers)\nbuiltins.AttributeError: \'NoneType\' object has no attribute
\'writeHeaders\'\n'


I found this similar bug report:
https://github.com/buildbot/buildbot/issues/4045
But I am using 19.2.1 twisted version..
Again, this is only triggered when I "stop" the locust io test.
Any suggestions?

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<div dir=3D"ltr">Hi,<div>=C2=A0 I have a twisted server. And I have been se=
eing this annoying issue.</div><div>Normally. when i develop and test it ou=
t. everything is fine..<br>But then I try to loadtest is via=C2=A0<a href=
=3D"https://locust.io/">https://locust.io/</a></div><div><br></div><div>Aga=
in, everything is fine.. until I &quot;stop&quot; the test.</div><div>Then,=
 I see this<br>&#39;Traceback (most recent call last):\n =C2=A0File &quot;/=
usr/local/Cellar/python/3.7.1/Frameworks/Python.framework/Versions/3.7/lib/=
python3.7/asyncio/events.py&quot;, line 88, in _run\n =C2=A0 =C2=A0self._co=
ntext.run(self._callback, *self._args)\n =C2=A0File &quot;/usr/local/lib/py=
thon3.7/site-packages/twisted/internet/defer.py&quot;, line 827, in adapt\n=
 =C2=A0 =C2=A0adapt.actual.callback(extracted)\n =C2=A0File &quot;/usr/loca=
l/lib/python3.7/site-packages/twisted/internet/defer.py&quot;, line 460, in=
 callback\n =C2=A0 =C2=A0self._startRunCallbacks(result)\n =C2=A0File &quot=
;/usr/local/lib/python3.7/site-packages/twisted/internet/defer.py&quot;, li=
ne 568, in _startRunCallbacks\n =C2=A0 =C2=A0self._runCallbacks()\n--- &lt;=
exception caught here&gt; ---\n =C2=A0File &quot;/usr/local/lib/python3.7/s=
ite-packages/twisted/internet/defer.py&quot;, line 654, in _runCallbacks\n =
=C2=A0 =C2=A0current.result =3D callback(current.result, *args, **kw)\n =C2=
=A0File=C2=A0</div><div>....</div><div>=C2=A0File &quot;/usr/local/lib/pyth=
on3.7/site-packages/twisted/web/server.py&quot;, line 238, in write\n =C2=
=A0 =C2=A0http.Request.write(self, data)\n =C2=A0File &quot;/usr/local/lib/=
python3.7/site-packages/twisted/web/http.py&quot;, line 1118, in write\n =
=C2=A0 =C2=A0self.channel.writeHeaders(version, code, reason, headers)\nbui=
ltins.AttributeError: \&#39;NoneType\&#39; object has no attribute \&#39;wr=
iteHeaders\&#39;\n&#39;<br></div><div><br></div><div><br></div><div>I found=
 this similar bug report:=C2=A0<a href=3D"https://github.com/buildbot/build=
bot/issues/4045">https://github.com/buildbot/buildbot/issues/4045</a></div>=
<div>But I am using=C2=A019.2.1 twisted version..</div><div>Again, this is =
only triggered when I &quot;stop&quot; the locust io test.</div><div>Any su=
ggestions?</div></div>

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