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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def decode_cli_arg(arg):
 """ Turn a bytestring provided by `argparse` into unicode. :param arg: The bytestring to decode. :return: The argument as a unicode object. :raises ValueError: If arg is None. """

    if arg is None:
        raise ValueError('Argument cannot be None')

    if sys.version_info.major == 3:
        # already decoded
        return arg

    return arg.decode(sys.getfilesystemencoding())