ros/rosdistro — pull request #4949 by po1 (2014-07-06 12:20:11+00:00)
Title: Remove empty rule (xulrunner: debian)

This was causing an error when running `rosdep db` on debian:

```
InvalidData: rosdep OS definition for [xulrunner-1.9.2:debian] must be a dictionary, string, or list: None
```