src/main/java/io/reactivex/Maybe.java
@CheckReturnValue
    @NonNull
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Single<T> switchIfEmpty(SingleSource<? extends T> other) {
        ObjectHelper.requireNonNull(other, "other is null");
        return RxJavaPlugins.onAssembly(new MaybeSwitchIfEmptySingle<T>(this, other));
    }
@CheckReturnValue
    @NonNull
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Single<T> switchIfEmpty(SingleSource<? extends T> other) {
        ObjectHelper.requireNonNull(other, "other is null");
        return RxJavaPlugins.onAssembly(new MaybeSwitchIfEmptySingle<T>(this, other));
    }
Returns a Single that emits the items emitted by the source Maybe or the item of an alternate
SingleSource if the current Maybe is empty.
<p>
<img width="640" height="445" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/switchifempty.m.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code switchIfEmpty} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>
<p>History: 2.1.4 - experimental
@param other
the alternate SingleSource to subscribe to if the main does not emit any items
@return  a Single that emits the items emitted by the source Maybe or the item of an
alternate SingleSource if the source Maybe is empty.
@since 2.2