src/main/java/io/reactivex/Observable.java
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Single<T> lastOrError() {
        return RxJavaPlugins.onAssembly(new ObservableLastSingle<T>(this, null));
    }
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Single<T> lastOrError() {
        return RxJavaPlugins.onAssembly(new ObservableLastSingle<T>(this, null));
    }
Returns a Single that emits only the last item emitted by this Observable or
signals a {@link NoSuchElementException} if this Observable is empty.
<p>
<img width="640" height="236" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/lastOrError.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code lastOrError} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>

@return a Single that emits only the last item emitted by the source ObservableSource.
If the source ObservableSource completes without emitting any items a {@link NoSuchElementException} will be thrown.
@see <a href="http://reactivex.io/documentation/operators/last.html">ReactiveX operators documentation: Last</a>