mailgun/shipper — pull request #9 by pchaussalet (2014-07-10 21:21:41+00:00)
Title: Fix null user on container creation

When creating a container without specifying a user kwarg, it sends a null value in the json payload, which prevent starting the container.
It can be reproduced using dockerfile/mongodb image.
I added a default empty value when accessing the kwarg to avoid sending null in the payload.