code: @CheckReturnValue
      @BackpressureSupport(BackpressureKind.FULL)
      @SchedulerSupport(SchedulerSupport.NONE)
      public final Flowable<T> onErrorReturnItem(final T item) {
          ObjectHelper.requireNonNull(item, "item is null");
          return onErrorReturn(Functions.justFunction(item));
      }
docs: Instructs a Publisher to emit an item (returned by a specified function) rather than invoking
  {@link Subscriber#onError onError} if it encounters an error.
  <p>
  <img width="640" height="310" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/onErrorReturn.png" alt="">
  <p>
  By default, when a Publisher encounters an error that prevents it from emitting the expected item to
  its {@link Subscriber}, the Publisher invokes its Subscriber's {@code onError} method, and then quits
  without invoking any more of its Subscriber's methods. The {@code onErrorReturn} method changes this
  behavior. If you pass a function ({@code resumeFunction}) to a Publisher's {@code onErrorReturn}
  method, if the original Publisher encounters an error, instead of invoking its Subscriber's
  {@code onError} method, it will instead emit the return value of {@code resumeFunction}.
  <p>
  You can use this to prevent errors from propagating or to supply fallback data should errors be
  encountered.
  <dl>
  <dt><b>Backpressure:</b></dt>
  <dd>The operator honors backpressure from downstream. The source {@code Publisher}s is expected to honor
  backpressure as well. If it this expectation is violated, the operator <em>may</em> throw
  {@code IllegalStateException} when the source {@code Publisher} completes or
  {@code MissingBackpressureException} is signaled somewhere downstream.</dd>
  <dt><b>Scheduler:</b></dt>
  <dd>{@code onErrorReturnItem} does not operate by default on a particular {@link Scheduler}.</dd>
  </dl>
  
  @param item
  the value that is emitted along with a regular onComplete in case the current
  Flowable signals an exception
  @return the original Publisher with appropriately modified behavior
  @see <a href="http://reactivex.io/documentation/operators/catch.html">ReactiveX operators documentation: Catch</a>