Comment 4 for bug 1510629

The issue seems to be related to a runtime failure to find the correct subnet for this IP:

2015-10-30 18:10:33 [-] Unhandled failure dispatching AMP command. This is probably a bug. Please ensure that this error is handled within application code or declared in the signature of the UpdateLeases command. [trusty-test:pid=11003:cmd=UpdateLeases:ask=19f]
 Traceback (most recent call last):
   File "/usr/lib/python2.7/threading.py", line 783, in __bootstrap
     self.__bootstrap_inner()
   File "/usr/lib/python2.7/threading.py", line 810, in __bootstrap_inner
     self.run()
   File "/usr/lib/python2.7/threading.py", line 763, in run
     self.__target(*self.__args, **self.__kwargs)
   File "/usr/lib/python2.7/dist-packages/provisioningserver/utils/twisted.py", line 791, in _worker
     return super(ThreadPool, self)._worker()
 --- <exception caught here> ---
   File "/usr/lib/python2.7/dist-packages/twisted/python/threadpool.py", line 191, in _worker
     result = context.call(ctx, function, *args, **kwargs)
   File "/usr/lib/python2.7/dist-packages/twisted/python/context.py", line 118, in callWithContext
     return self.currentContext().callWithContext(ctx, func, *args, **kw)
   File "/usr/lib/python2.7/dist-packages/twisted/python/context.py", line 81, in callWithContext
     return func(*args,**kw)
   File "/usr/lib/python2.7/dist-packages/provisioningserver/utils/twisted.py", line 200, in wrapper
     return func(*args, **kwargs)
   File "/usr/lib/python2.7/dist-packages/maasserver/utils/orm.py", line 480, in call_within_transaction
     return func_outside_txn(*args, **kwargs)
   File "/usr/lib/python2.7/dist-packages/maasserver/utils/orm.py", line 307, in retrier
     return func(*args, **kwargs)
   File "/usr/lib/python2.7/dist-packages/django/db/transaction.py", line 339, in inner
     return func(*args, **kwargs)
   File "/usr/lib/python2.7/dist-packages/maasserver/rpc/leases.py", line 51, in update_leases
     StaticIPAddress.objects.update_leases(nodegroup, leases)
   File "/usr/lib/python2.7/dist-packages/maasserver/models/staticipaddress.py", line 451, in update_leases
     subnet_family = subnet.get_ipnetwork().version
 exceptions.AttributeError: 'NoneType' object has no attribute 'get_ipnetwork'