def METHOD_NAME(self, field_name_with_type: str) -> Tuple[str, Optional[str]]:
    type_delim_idx = field_name_with_type.find(self._TYPE_DELIM)
    if type_delim_idx > 0:
        field_name = field_name_with_type[:type_delim_idx]
        field_type = field_name_with_type[type_delim_idx + 1 :]
    elif type_delim_idx == 0:
        self._parse_error(f'"{field_name_with_type}", field name is empty!')
    else:
        field_name = field_name_with_type
        field_type = None
    # pyre-fixme[61]: `field_name` may not be initialized here.
    # pyre-fixme[61]: `field_type` may not be initialized here.
    return field_name, field_type