code: public static Schedulers stop(String schedulerId) {
          createSingleton();
          // if (instance.runningSchedullers.isEmpty()) {
          // throw new IllegalStateException("No schedulers available.");
          // }
  
          ScheduledFuture<?> future = instance.runningSchedullers.get(schedulerId);
          if (future == null) {
              throw new IllegalStateException("No schedulers match with given id.");
          }
          future.cancel(true);
          Schedulers.decreaseNoOfSchedullers();
          Schedulers.decreaseNoOfRunningSchedullers();
  
          return instance;
      }
docs: Stop.
  
  @param schedulerId
  the scheduler id
  @return the schedulers