def _fallback(self, section_name, pref_name):
        """
        Create a fallback preference object,
        This is used when you have model instances that do not match
        any registered preferences, see #41
        """
        message = (
            'Creating a fallback preference with ' +
            'section "{}" and name "{}".' +
            'This means you have preferences in your database that ' +
            'don\'t match any registered preference. ' +
            'If you want to delete these entries, please refer to the ' +
            'documentation: https://django-dynamic-preferences.readthedocs.io/en/latest/lifecycle.html')  # NOQA
        warnings.warn(message.format(section_name, pref_name))

        class Fallback(MissingPreference):
            section = Section(name=section_name) if section_name else None
            name = pref_name
            default = ''
            help_text = 'Obsolete: missing in registry'

        return Fallback()
Create a fallback preference object,
        This is used when you have model instances that do not match
        any registered preferences, see #41