code: @CheckReturnValue
      @BackpressureSupport(BackpressureKind.PASS_THROUGH)
      @SchedulerSupport(SchedulerSupport.NONE)
      public final Flowable<T> mergeWith(@NonNull CompletableSource other) {
          ObjectHelper.requireNonNull(other, "other is null");
          return RxJavaPlugins.onAssembly(new FlowableMergeWithCompletable<T>(this, other));
      }
docs: Relays the items of this Flowable and completes only when the other CompletableSource completes
  as well.
  <p>
  <img width="640" height="380" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/merge.png" alt="">
  <dl>
  <dt><b>Backpressure:</b></dt>
  <dd>The operator doesn't interfere with backpressure which is determined by the source {@code Publisher}'s backpressure
  behavior.</dd>
  <dt><b>Scheduler:</b></dt>
  <dd>{@code mergeWith} does not operate by default on a particular {@link Scheduler}.</dd>
  </dl>
  <p>History: 2.1.10 - experimental
  @param other the {@code CompletableSource} to await for completion
  @return the new Flowable instance
  @since 2.2