I ran 'git cl issue 0' to reset the issue number in my branch. It work, I then forgot I ran it and ran it a second time and got the following traceback.

Traceback (most recent call last):
  File "/usr/local/google/home/dsinclair/Development/depot_tools/git_cl.py", line 6089, in <module>
    sys.exit(main(sys.argv[1:]))
  File "/usr/local/google/home/dsinclair/Development/depot_tools/git_cl.py", line 6071, in main
    return dispatcher.execute(OptionParser(), argv)
  File "/usr/local/google/home/dsinclair/Development/depot_tools/subcommand.py", line 252, in execute
    return command(parser, args[1:])
  File "/usr/local/google/home/dsinclair/Development/depot_tools/git_cl.py", line 4500, in CMDissue
    cl.SetIssue(issue.issue)
  File "/usr/local/google/home/dsinclair/Development/depot_tools/git_cl.py", line 1475, in SetIssue
    if git_footers.get_footer_change_id(desc):
  File "/usr/local/google/home/dsinclair/Development/depot_tools/git_footers.py", line 85, in get_footer_change_id
    return parse_footers(message).get(normalize_name('Change-Id'), [])
  File "/usr/local/google/home/dsinclair/Development/depot_tools/git_footers.py", line 35, in parse_footers
    _, _, parsed_footers = split_footers(message)
  File "/usr/local/google/home/dsinclair/Development/depot_tools/git_footers.py", line 65, in split_footers
    message_lines = list(message.splitlines())
AttributeError: 'NoneType' object has no attribute 'splitlines'