@classmethod
def __group_params(cls, sparam, mparam, sparam_name, mparam_name, default=
    None, allmstr=None):
    """Create list with either the singular or multiple valued parameter's value(s).

        This method allows only one or the other parameter to be defined, and returns a list
        containing whatever it finds. If neither parameter is defined, the specified default is
        instead returned.
        """
    if sparam is None and mparam is None:
        return default
    if sparam is not None:
        if mparam is not None:
            raise ValueError(
                f'{sparam_name} and {mparam_name} cannot both be defined')
        return [sparam]
    if allmstr is not None and mparam == allmstr:
        return mparam
    return list(mparam)
