src/main/java/io/reactivex/Flowable.java
@CheckReturnValue
    @BackpressureSupport(BackpressureKind.PASS_THROUGH)
    @SchedulerSupport(SchedulerSupport.NONE)
    @SuppressWarnings("unchecked")
    public static <T> Flowable<T> never() {
        return RxJavaPlugins.onAssembly((Flowable<T>) FlowableNever.INSTANCE);
    }
@CheckReturnValue
    @BackpressureSupport(BackpressureKind.PASS_THROUGH)
    @SchedulerSupport(SchedulerSupport.NONE)
    @SuppressWarnings("unchecked")
    public static <T> Flowable<T> never() {
        return RxJavaPlugins.onAssembly((Flowable<T>) FlowableNever.INSTANCE);
    }
Returns a Flowable that never sends any items or notifications to a {@link Subscriber}.
<p>
<img width="640" height="185" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/never.png" alt="">
<p>
This Publisher is useful primarily for testing purposes.
<dl>
<dt><b>Backpressure:</b></dt>
<dd>This source doesn't produce any elements and effectively ignores downstream backpressure.</dd>
<dt><b>Scheduler:</b></dt>
<dd>{@code never} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>

@param <T>
the type of items (not) emitted by the Publisher
@return a Flowable that never emits any items or sends any notifications to a {@link Subscriber}
@see <a href="http://reactivex.io/documentation/operators/empty-never-throw.html">ReactiveX operators documentation: Never</a>