code: @CheckReturnValue
      @SchedulerSupport(SchedulerSupport.NONE)
      public final <U> Observable<U> flattenAsObservable(final Function<? super T, ? extends Iterable<? extends U>> mapper) {
          ObjectHelper.requireNonNull(mapper, "mapper is null");
          return RxJavaPlugins.onAssembly(new MaybeFlatMapIterableObservable<T, U>(this, mapper));
      }
docs: Returns an Observable that maps a success value into an Iterable and emits its items.
  <p>
  <img width="640" height="373" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/flattenAsObservable.png" alt="">
  <dl>
  <dt><b>Scheduler:</b></dt>
  <dd>{@code flattenAsObservable} does not operate by default on a particular {@link Scheduler}.</dd>
  </dl>
  
  @param <U>
  the type of item emitted by the resulting Iterable
  @param mapper
  a function that returns an Iterable sequence of values for when given an item emitted by the
  source Maybe
  @return the new Observable instance
  @see <a href="http://reactivex.io/documentation/operators/flatmap.html">ReactiveX operators documentation: FlatMap</a>