Operating system

Ubuntu 16.04.3

nbgrader --version

Python version 3.6.3 |Anaconda custom (64-bit)| (default, Oct 13 2017, 12:02:49)
[GCC 7.2.0]
nbgrader version 0.5.4

jupyterhub --version (if used with JupyterHub)

0.8.1

jupyter notebook --version

5.2.1

Expected behavior

The Autograde button of a submission in the "Manage Submissions" page should work even if the student ID contains Backslashes.

Actual behavior

The Autograde button of a submission in the "Manage Submissions" page don't work if the student ID contains Backslashes.
In my case the Backslashe comes from the fact that all student accounts are AD Domain accounts.

Steps to reproduce the behavior

• Create a student with a backslash in his ID.
• Make him submit an assignment with the web interface.
• Collect the assignements with the web interface
• Try to autograde the backslashed student with the web interface