How to use the routemaster.config.model.NoNextStates function in routemaster

class NoNextStates(NamedTuple):
    """Represents the lack of a next state to progress to."""

    def next_state_for_label(self, label_context: Any) -> str:
        """Invalid to call, raise an exception."""
        raise RuntimeError(
            "Attempted to progress from a state with no next state",
        )

    def all_destinations(self) -> Iterable[str]:
        """Returns no states."""
        return []


NextStates = Union[ConstantNextState, ContextNextStates, NoNextStates]


class Gate(NamedTuple):
    """
    A state that restricts a label from moving based on an exit condition.

    Gates cannot perform an action.
    """
    name: str
    next_states: NextStates

    exit_condition: ExitConditionProgram
    triggers: Iterable[Trigger]

    @property
    def metadata_triggers(self) -> List[MetadataTrigger]:

def _load_next_states(
    path: Path,
    yaml_next_states: Optional[Yaml],
    feed_names: List[str],
) -> NextStates:

    if yaml_next_states is None:
        return NoNextStates()

    if isinstance(yaml_next_states, str):
        return _load_constant_next_state(path, {'state': yaml_next_states})
    if yaml_next_states['type'] == 'constant':
        return _load_constant_next_state(path, yaml_next_states)
    elif yaml_next_states['type'] == 'context':  # pragma: no branch
        return _load_context_next_states(path, yaml_next_states, feed_names)
    else:
        raise ConfigError(  # pragma: no cover
            f"Next state config at path {'.'.join(path)} must be of type "
            f"'constant' or 'context'",
        ) from None