docs: public Future<?> schedule(Runnable task, long delay, TimeUnit unit)
      {
          Preconditions.checkState(isOpen.get(), "CloseableExecutorService is closed");
  
          InternalFutureTask<Void> futureTask = new InternalFutureTask<Void>(new FutureTask<Void>(task, null));
          scheduledExecutorService.schedule(futureTask, delay, unit);
          return futureTask;
      }