cubicweb #1772125 exceptions.AttributeError: 'NoneType' object has no attribute 'check' [resolved]

Seen from time to time in the logs of all-in-one instances:

2011-06-22 10:08:32 - (cubicweb.web) INFO: publish "/case/170995" (adminfcf1974d758946978eb65069bf3fd7f0, form params: [])
Unhandled error in Deferred:
Traceback (most recent call last):
 File "/usr/lib/python2.6/dist-packages/twisted/internet/", line 1165, in run
 File "/usr/lib/python2.6/dist-packages/twisted/internet/", line 1174, in mainLoop
 File "/usr/lib/python2.6/dist-packages/twisted/internet/", line 796, in runUntilCurrent
   call.func(*call.args, **
 File "/usr/lib/python2.6/dist-packages/twisted/internet/", line 194, in __call__
   d = defer.maybeDeferred(self.f, *self.a, **
--- <exception caught here> ---
 File "/usr/lib/python2.6/dist-packages/twisted/internet/", line 125, in maybeDeferred
   result = f(*args, **kw)
 File "/home/alf/cubicweb/cubicweb/web/", line 173, in clean_sessions
 File "/home/alf/cubicweb/cubicweb/web/", line 73, in clean_sessions
   last_usage_time = session.cnx.check()
exceptions.AttributeError: 'NoneType' object has no attribute 'check'
done in3.12.9
load left0.000
closed by#d3459fe041f0 [web session] fix bad cleanup of session without a connection set. Closes #1772125