def parse_protocol_string(arg):
    """Retrieve protocol and options from argument."""
    if not arg:
        return None, u''
    argsplit = arg.split(u':', 1)
    if len(argsplit) == 1:
        addr, val = None, argsplit[0]
    else:
        addr, val = argsplit[0].upper(), u''.join(argsplit[1:])
    return addr, val
