Generate random series of passport.

        :param year: Year of manufacture.
        :type year: int or None
        :return: Series.

        :Example:
            02 15.

def passport_series(self, year: int = None) -> str:
        """Generate random series of passport.

        :param year: Year of manufacture.
        :type year: int or None
        :return: Series.

        :Example:
            02 15.
        """
        if not year:
            year = self.random.randint(10, 18)

        region = self.random.randint(1, 99)
        return '{:02d} {}'.format(region, year)