Comment 3 for bug 1420046

New assertion confirms the theory, eg. OOPS-0858ab81859c279c8b8d55322b57402c:

Traceback (most recent call last):
  File "/srv/launchpadlibrarian.net/production/launchpad3-rev-17355/eggs/Twisted-13.0.0-py2.7-linux-x86_64.egg/twisted/internet/defer.py", line 421, in errback
    self._startRunCallbacks(fail)
  File "/srv/launchpadlibrarian.net/production/launchpad3-rev-17355/eggs/Twisted-13.0.0-py2.7-linux-x86_64.egg/twisted/internet/defer.py", line 488, in _startRunCallbacks
    self._runCallbacks()
  File "/srv/launchpadlibrarian.net/production/launchpad3-rev-17355/eggs/Twisted-13.0.0-py2.7-linux-x86_64.egg/twisted/internet/defer.py", line 575, in _runCallbacks
    current.result = callback(current.result, *args, **kw)
  File "/srv/launchpadlibrarian.net/production/launchpad3-rev-17355/eggs/Twisted-13.0.0-py2.7-linux-x86_64.egg/twisted/internet/defer.py", line 1126, in gotResult
    _inlineCallbacks(r, g, deferred)
--- <exception caught here> ---
  File "/srv/launchpadlibrarian.net/production/launchpad3-rev-17355/eggs/Twisted-13.0.0-py2.7-linux-x86_64.egg/twisted/internet/defer.py", line 1068, in _inlineCallbacks
    result = result.throwExceptionIntoGenerator(g)
  File "/srv/launchpadlibrarian.net/production/launchpad3-rev-17355/eggs/Twisted-13.0.0-py2.7-linux-x86_64.egg/twisted/python/failure.py", line 389, in throwExceptionIntoGenerator
    return g.throw(self.type, self.value, self.tb)
  File "/srv/launchpadlibrarian.net/production/launchpad3-rev-17355/lib/lp/services/librarianserver/web.py", line 322, in resumeProducing
    data = yield self.fileObject.read(self.bufferSize)
  File "/srv/launchpadlibrarian.net/production/launchpad3-rev-17355/eggs/Twisted-13.0.0-py2.7-linux-x86_64.egg/twisted/internet/defer.py", line 1070, in _inlineCallbacks
    result = g.send(result)
  File "/srv/launchpadlibrarian.net/production/launchpad3-rev-17355/lib/lp/services/librarianserver/storage.py", line 150, in read
    swift.connection_pool.put(self._swift_connection)
  File "/srv/launchpadlibrarian.net/production/launchpad3-rev-17355/lib/lp/services/librarianserver/swift.py", line 351, in put
    "%r is not a swiftclient Connection." % swift_connection)
exceptions.AssertionError: None is not a swiftclient Connection.