problem using jgit

I've setup a simple test class that integrates jgit to clone a git 
repository. However I'm getting a NullPointerError when 
RevWalk.parseAny ends up producing a null object id.

The code and the stack trace for the error are here:

   http://pastie.org/237711

This problem occurs using the jgit from the master branch from this repo:

   git://repo.or.cz/egit.git