def GetCustomJsonFieldMapping(message_type, python_name=None, json_name=None):
    """Return the appropriate remapping for the given field, or None."""
    return _FetchRemapping(message_type, 'field',
                           python_name=python_name, json_name=json_name,
                           mappings=_JSON_FIELD_MAPPINGS)
Return the appropriate remapping for the given field, or None.