docs: public String addMpNews(MpNews mpNews) {
          String url = WxEndpoint.get("url.material.mpnews.add");
  
          String json = JsonMapper.nonEmptyMapper().toJson(mpNews);
          logger.info("add mpnews: {}", json);
          String response =  wxClient.post(url, json);
          Map<String, Object> result = JsonMapper.defaultMapper().json2Map(response);
          if (result.containsKey("media_id")) {
              return result.get("media_id").toString();
          } else {
              logger.warn("mpnews add failed: {}", response);
              throw new WxRuntimeException(999, response);
          }
      }