def _unquote_or_none(s):
    if s is None:
        return s
    return escape.url_unescape(s, encoding=None, plus=False)
None-safe wrapper around url_unescape to handle unamteched optional
dataset/ETHPy150Open RobotWebTools/rosbridge_suite/rosbridge_server/src/tornado/web.py/_unquote_or_none