code: @Override
      public ScheduledExecutorService getScheduler() {
          ScheduledExecutorService sRef = executorService.get();
          if (sRef == null) {
              throw new IllegalStateException("ScheduledExecutorService service is unavailable");
          }
          return sRef;
      }
docs: Retrieve the scheduler
  
  @return bound ScheduledExecutorService
  @throws IllegalStateException if the ScheduledExecutorService is not found