buildd-manager regression: 'NoneType' object has no attribute 'flush'

[Colin Watson]

After deploying f759833f01c7f0b01b31b10cf317a55893ebb0ad to production (previously bbfee60eef9f7fd8d30b24b3f53e75656e4d5fb0), buildd-manager started failing builds as follows:

2021-02-22 17:29:47+0000 [QueryProtocol,client] Traceback (most recent call last):
2021-02-22 17:29:47+0000 [QueryProtocol,client] File "/srv/launchpad.net/codelines/soyuz-production-rev-f759833f01c7f0b01b31b10cf317a55893ebb0ad/env/local/lib/python2.7/site-packages/twisted/internet/defer.py", line 460, in callback
2021-02-22 17:29:47+0000 [QueryProtocol,client] self._startRunCallbacks(result)
2021-02-22 17:29:47+0000 [QueryProtocol,client] File "/srv/launchpad.net/codelines/soyuz-production-rev-f759833f01c7f0b01b31b10cf317a55893ebb0ad/env/local/lib/python2.7/site-packages/twisted/internet/defer.py", line 568, in _startRunCal
lbacks
2021-02-22 17:29:47+0000 [QueryProtocol,client] self._runCallbacks()
2021-02-22 17:29:47+0000 [QueryProtocol,client] File "/srv/launchpad.net/codelines/soyuz-production-rev-f759833f01c7f0b01b31b10cf317a55893ebb0ad/env/local/lib/python2.7/site-packages/twisted/internet/defer.py", line 654, in _runCallback
s
2021-02-22 17:29:47+0000 [QueryProtocol,client] current.result = callback(current.result, *args, **kw)
2021-02-22 17:29:47+0000 [QueryProtocol,client] File "/srv/launchpad.net/codelines/soyuz-production-rev-f759833f01c7f0b01b31b10cf317a55893ebb0ad/env/local/lib/python2.7/site-packages/twisted/internet/defer.py", line 1475, in gotResult
2021-02-22 17:29:47+0000 [QueryProtocol,client] _inlineCallbacks(r, g, status)
2021-02-22 17:29:47+0000 [QueryProtocol,client] --- <exception caught here> ---
2021-02-22 17:29:47+0000 [QueryProtocol,client] File "/srv/launchpad.net/codelines/soyuz-production-rev-f759833f01c7f0b01b31b10cf317a55893ebb0ad/env/local/lib/python2.7/site-packages/twisted/internet/defer.py", line 1418, in _inlineCall
backs
2021-02-22 17:29:47+0000 [QueryProtocol,client] result = g.send(result)
2021-02-22 17:29:47+0000 [QueryProtocol,client] File "/srv/launchpad.net/codelines/soyuz-production-rev-f759833f01c7f0b01b31b10cf317a55893ebb0ad/lib/lp/buildmaster/manager.py", line 631, in scan
2021-02-22 17:29:47+0000 [QueryProtocol,client] expected_cookie = self.getExpectedCookie(vitals)
2021-02-22 17:29:47+0000 [QueryProtocol,client] File "/srv/launchpad.net/codelines/soyuz-production-rev-f759833f01c7f0b01b31b10cf317a55893ebb0ad/lib/lp/buildmaster/manager.py", line 588, in getExpectedCookie
2021-02-22 17:29:47+0000 [QueryProtocol,client] if vitals.build_queue != self._cached_build_queue:
2021-02-22 17:29:47+0000 [QueryProtocol,client] File "/srv/launchpad.net/codelines/soyuz-production-rev-f759833f01c7f0b01b31b10cf317a55893ebb0ad/lib/lp/services/database/stormbase.py", line 50, in __ne__
2021-02-22 17:29:47+0000 [QueryProtocol,client] return not (self == other)
2021-02-22 17:29:47+0000 [QueryProtocol,client] File "/srv/launchpad.net/codelines/soyuz-production-rev-f759833f01c7f0b01b31b10cf317a55893ebb0ad/lib/lp/services/database/stormbase.py", line 43, in __eq__
2021-02-22 17:29:47+0000 [QueryProtocol,client] Store.of(other).flush()
2021-02-22 17:29:47+0000 [QueryProtocol,client] exceptions.AttributeError: 'NoneType' object has no attribute 'flush'

This seems to be due to https://code.launchpad.net/~cjwatson/launchpad/+git/launchpad/+merge/398087, although I don't yet know why.