@classmethod
def _normalize_unit(cls, unit):
    """Resolve a unit to its real name if it's an alias.

        :param unit str: the unit to normalize
        :return: the normalized unit, or None one isn't found
        :rtype: Union[None, str]
        """
    if unit in cls.UNITS_IN_SECONDS:
        return unit
    return cls.UNIT_ALIASES_REVERSE.get(unit, None)
