src/main/java/io/reactivex/Flowable.java
@CheckReturnValue
    @BackpressureSupport(BackpressureKind.UNBOUNDED_IN)
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Completable ignoreElements() {
        return RxJavaPlugins.onAssembly(new FlowableIgnoreElementsCompletable<T>(this));
    }
@CheckReturnValue
    @BackpressureSupport(BackpressureKind.UNBOUNDED_IN)
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Completable ignoreElements() {
        return RxJavaPlugins.onAssembly(new FlowableIgnoreElementsCompletable<T>(this));
    }
Ignores all items emitted by the source Publisher and only calls {@code onComplete} or {@code onError}.
<p>
<img width="640" height="305" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/ignoreElements.png" alt="">
<dl>
<dt><b>Backpressure:</b></dt>
<dd>This operator ignores backpressure as it doesn't emit any elements and consumes the source {@code Publisher}
in an unbounded manner (i.e., no backpressure is applied to it).</dd>
<dt><b>Scheduler:</b></dt>
<dd>{@code ignoreElements} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>

@return a Completable that only calls {@code onComplete} or {@code onError}, based on which one is
called by the source Publisher
@see <a href="http://reactivex.io/documentation/operators/ignoreelements.html">ReactiveX operators documentation: IgnoreElements</a>