Unable to restart awestruct docker image

When running awestruct via docker there are occasional problems. This must be due to some state in the volumes but I'm currently unable to give accurate instructions to reproduce.

The best I have is:
1)Start docker using "./control.rb --run-the-stack"
2)Stop the system using ctrl-c
3)Start the system again using "./control.rb --run-the-stack".

Awestruct will run for some time, then fail with the message

Internal Server Error

undefined method `[]' for nil:NilClass
WEBrick/1.3.1 (Ruby/2.1.2/2014-05-08) at docker:32768

The way to rectify is to kill then remove the containers.