docs: public Channel findById(Long channelId) {
          Assert.assertNotNull(channelId);
          List<Channel> channels = listByIds(channelId);
          if (channels.size() != 1) {
              String exceptionCause = "query channelId:" + channelId + " return null.";
              logger.error("ERROR ## " + exceptionCause);
              throw new ManagerException(exceptionCause);
          }
          return channels.get(0);
      }