:param username: the username. If None, the username of the currently logged in user is taken
        :return: True if the user is superadmin, False else

def user_is_superadmin(self, username=None):
        """
        :param username: the username. If None, the username of the currently logged in user is taken
        :return: True if the user is superadmin, False else
        """
        if username is None:
            username = self.session_username()

        return username in self._superadmins