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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_rich_menu_id_of_user(self, user_id, timeout=None):
 """Call get rich menu ID of user API. https://developers.line.me/en/docs/messaging-api/reference/#get-rich-menu-id-of-user :param str user_id: IDs of the user :param timeout: (optional) How long to wait for the server to send data before giving up, as a float, or a (connect timeout, read timeout) float tuple. Default is self.http_client.timeout :type timeout: float | tuple(float, float) :rtype: str :return: rich menu id """

        response = self._get(
            '/v2/bot/user/{user_id}/richmenu'.format(user_id=user_id),
            timeout=timeout
        )

        return response.json.get('richMenuId')