def rvnr(self, birthdate: Optional[date] = None) -> str:
        """
        Pension insurance number (German: "Rentenversicherungsnummer", abbr. "RVNR")

        Source: https://de.wikipedia.org/wiki/Versicherungsnummer

        :return: A valid German pension insurance number
        """
        _birthdate = birthdate or self.generator.date_object()
        format: str = f"##{_birthdate:%d%m%y}?##"
        rvnr: str = self.bothify(format, letters=ascii_uppercase)

        return rvnr + self.__get_rvnr_checkdigit(rvnr)

        Pension insurance number (German: "Rentenversicherungsnummer", abbr. "RVNR")

        Source: https://de.wikipedia.org/wiki/Versicherungsnummer

        :return: A valid German pension insurance number
        
faker/providers/ssn/de_DE/__init__.py