src/main/java/io/reactivex/Single.java
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    @SuppressWarnings("unchecked")
    public static <T> Single<T> never() {
        return RxJavaPlugins.onAssembly((Single<T>) SingleNever.INSTANCE);
    }
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    @SuppressWarnings("unchecked")
    public static <T> Single<T> never() {
        return RxJavaPlugins.onAssembly((Single<T>) SingleNever.INSTANCE);
    }
Returns a singleton instance of a never-signalling Single (only calls onSubscribe).
<p>
<img width="640" height="244" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Single.never.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code never} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>
@param <T> the target value type
@return the singleton never instance
@since 2.0