Catch the BadName exception raised by newer GitPython and gitdb versions
while ensuring that we still retain compatibility with older versions
that did not either contain this exception nor raise it.
To handle a new exception where it doesn't exist in the older codebase
simply set the value to None as except has no problem in matching
against non-existing exceptions.
Change-Id: Idf1f3e776317ad7a346364b9fadb4bc613bf2673
964d5c784e