docs: public Timer add(long interval, Handler handler, Object... args)
      {
          if (handler == null) {
              return null;
          }
          Utils.checkArgument(interval > 0, "Delay of a timer has to be strictly greater than 0");
          final Timer timer = new Timer(this, interval, handler, args);
          final boolean rc = insert(timer);
          assert (rc);
          return timer;
      }