code: @CheckReturnValue
      @SchedulerSupport(SchedulerSupport.NONE)
      public static Completable mergeDelayError(Iterable<? extends CompletableSource> sources) {
          ObjectHelper.requireNonNull(sources, "sources is null");
          return RxJavaPlugins.onAssembly(new CompletableMergeDelayErrorIterable(sources));
      }
docs: Returns a Completable that subscribes to all Completables in the source sequence and delays
  any error emitted by either the sources observable or any of the inner Completables until all of
  them terminate in a way or another.
  <p>
  <img width="640" height="475" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Completable.mergeDelayError.png" alt="">
  <dl>
  <dt><b>Scheduler:</b></dt>
  <dd>{@code mergeDelayError} does not operate by default on a particular {@link Scheduler}.</dd>
  </dl>
  @param sources the sequence of Completables
  @return the new Completable instance
  @throws NullPointerException if sources is null