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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 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)