def fiscal_code(self, gender: Optional[Gender] = None) -> str:
        """Return a random fiscal code.

        :param gender: Gender's enum object.
        :return: Fiscal code.

        Example:
            RSSMRA66R05D612U
        """
        code = ''.join(self.random.choices(string.ascii_uppercase, k=6))

        code += self.random.custom_code(mask='##')

        month_codes = self._data['fiscal_code']['month_codes']
        code += self.random.choice(month_codes)

        birth_day = self.random.randint(101, 131)
        self._validate_enum(gender, Gender)
        if gender == Gender.FEMALE:
            birth_day += 40
        code += str(birth_day)[1:]

        city_letters = self._data['fiscal_code']['city_letters']
        code += self.random.choice(city_letters)
        code += self.random.custom_code(mask='###@')

        return code
Return a random fiscal code.

        :param gender: Gender's enum object.
        :return: Fiscal code.

        Example:
            RSSMRA66R05D612U