code: @CheckReturnValue
      @SchedulerSupport(SchedulerSupport.NONE)
      public final Maybe<T> doFinally(Action onFinally) {
          ObjectHelper.requireNonNull(onFinally, "onFinally is null");
          return RxJavaPlugins.onAssembly(new MaybeDoFinally<T>(this, onFinally));
      }
docs: Calls the specified action after this Maybe signals onSuccess, onError or onComplete or gets disposed by
  the downstream.
  <p>In case of a race between a terminal event and a dispose call, the provided {@code onFinally} action
  is executed once per subscription.
  <p>Note that the {@code onFinally} action is shared between subscriptions and as such
  should be thread-safe.
  <dl>
  <dt><b>Scheduler:</b></dt>
  <dd>{@code doFinally} does not operate by default on a particular {@link Scheduler}.</dd>
  </dl>
  <p>History: 2.0.1 - experimental
  @param onFinally the action called when this Maybe terminates or gets disposed
  @return the new Maybe instance
  @since 2.1