:param str section: Config section
        :param str key: Config key

def _add_dot_key(self, section, key=None):
        """
        :param str section: Config section
        :param str key: Config key
        """
        if key:
            self._dot_keys[self._to_dot_key(section, key)] = (section, key)
        else:
            self._dot_keys[self._to_dot_key(section)] = section