code: @CheckReturnValue
      @SchedulerSupport(SchedulerSupport.NONE)
      public final Single<T> onErrorReturnItem(final T value) {
          ObjectHelper.requireNonNull(value, "value is null");
          return RxJavaPlugins.onAssembly(new SingleOnErrorReturn<T>(this, null, value));
      }
docs: Signals the specified value as success in case the current Single signals an error.
  <p>
  <img width="640" height="451" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Single.onErrorReturnItem.png" alt="">
  <dl>
  <dt><b>Scheduler:</b></dt>
  <dd>{@code onErrorReturnItem} does not operate by default on a particular {@link Scheduler}.</dd>
  </dl>
  @param value the value to signal if the current Single fails
  @return the new Single instance
  @since 2.0