docs: public static void addLoggerToGroup(Logger logger, String group) {
          if (logger == null)
              throw new NullPointerException("logger");
          if (group == null)
              throw new NullPointerException("group");
          if (!(logger instanceof WsLogger))
              throw new IllegalArgumentException("logger");
  
          WsLogger wsLogger = (WsLogger) logger;
          wsLogger.addGroup(group);
      }