Description of problem:
``fedpkg tag -l'' with no more arguments prints a traceback:

Traceback (most recent call last):
  File "/usr/bin/fedpkg", line 1495, in <module>
    args.command(args)
  File "/usr/bin/fedpkg", line 721, in tag
    pyfedpkg.list_tag(args.tag)
  File "/usr/lib/python2.7/site-packages/pyfedpkg/__init__.py", line 750, in list_tag
    _run_command(cmd)
  File "/usr/lib/python2.7/site-packages/pyfedpkg/__init__.py", line 210, in _run_command
    ' '.join(cmd))
TypeError: sequence item 3: expected string, NoneType found


Version-Release number of selected component (if applicable):
fedpkg-0.5.9.2-2.fc14.noarch


How reproducible:
Always


Steps to Reproduce:
1. fedpkg tag -l
The error occurs whether inside a git repository or not.

  
Actual results:
Traceback (see description)


Expected results:
A list of git tags