code: @CheckReturnValue
      @SchedulerSupport(SchedulerSupport.NONE)
      public final Maybe<T> doOnSubscribe(Consumer<? super Disposable> onSubscribe) {
          return RxJavaPlugins.onAssembly(new MaybePeek<T>(this,
                  ObjectHelper.requireNonNull(onSubscribe, "onSubscribe is null"),
                  Functions.emptyConsumer(), // onSuccess
                  Functions.emptyConsumer(), // onError
                  Functions.EMPTY_ACTION,    // onComplete
                  Functions.EMPTY_ACTION,    // (onSuccess | onError | onComplete)
                  Functions.EMPTY_ACTION     // dispose
          ));
      }
docs: Calls the shared consumer with the Disposable sent through the onSubscribe for each
  MaybeObserver that subscribes to the current Maybe.
  <dl>
  <dt><b>Scheduler:</b></dt>
  <dd>{@code doOnSubscribe} does not operate by default on a particular {@link Scheduler}.</dd>
  </dl>
  @param onSubscribe the consumer called with the Disposable sent via onSubscribe
  @return the new Maybe instance