def get_expected_update_frequency(self):
        # type: () -> Optional[str]
        """Get expected update frequency (in textual rather than numeric form)

        Returns:
            Optional[str]: Update frequency in textual form or None if the update frequency doesn't exist or is blank.
        """
        days = self.data.get('data_update_frequency', None)
        if days:
            return Dataset.transform_update_frequency(days)
        else:
            return None