praekelt/vumi — pull request #452 by hodgestar (2013-03-01 09:33:11+00:00)
Title: SMPP transport needs to handle nacks without a reason more gracefully.

Sometimes we receive a nack response without a reason from the SMPP bind.
In this case the `nack_reason` is `None` which means the validation in `TransportEvent` breaks.

See https://gist.github.com/902fa36daac35b485c7a