On Windows, calling:

git cl upstream winFontUniqueMatchingNoUma

leads to the following traceback:

Traceback (most recent call last):
  File "C:\src\depot_tools\metrics.py", line 262, in print_notice_and_exit
    yield
  File "C:\src\depot_tools\\git_cl.py", line 5538, in <module>
    sys.exit(main(sys.argv[1:]))
  File "C:\src\depot_tools\\git_cl.py", line 5520, in main
    return dispatcher.execute(OptionParser(), argv)
  File "C:\src\depot_tools\subcommand.py", line 252, in execute
    return command(parser, args[1:])
  File "C:\src\depot_tools\metrics.py", line 247, in _inner
    return self._collect_metrics(func, command_name, *args, **kwargs)
  File "C:\src\depot_tools\metrics.py", line 200, in _collect_metrics
    result = func(*args, **kwargs)
  File "C:\src\depot_tools\\git_cl.py", line 4952, in CMDupstream
    RunGit(['branch', '--set-upstream-to', args[0], branch])
  File "C:\src\depot_tools\\git_cl.py", line 139, in RunGit
    return RunCommand(['git'] + args, **kwargs)
  File "C:\src\depot_tools\\git_cl.py", line 127, in RunCommand
    return subprocess2.check_output(args, shell=shell, **kwargs)
  File "C:\src\depot_tools\subprocess2.py", line 528, in check_output
    return check_call_out(args, stdout=PIPE, **kwargs)[0]
  File "C:\src\depot_tools\subprocess2.py", line 488, in check_call_out
    out, returncode = communicate(args, **kwargs)
  File "C:\src\depot_tools\subprocess2.py", line 462, in communicate
    proc = Popen(args, **kwargs)
  File "C:\src\depot_tools\subprocess2.py", line 214, in __init__
    tmp_str = ' '.join(args)
TypeError: sequence item 4: expected string, NoneType found