src/main/java/io/reactivex/Flowable.java
@CheckReturnValue
    @NonNull
    @BackpressureSupport(BackpressureKind.FULL)
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Flowable<T> switchIfEmpty(Publisher<? extends T> other) {
        ObjectHelper.requireNonNull(other, "other is null");
        return RxJavaPlugins.onAssembly(new FlowableSwitchIfEmpty<T>(this, other));
    }
@CheckReturnValue
    @NonNull
    @BackpressureSupport(BackpressureKind.FULL)
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Flowable<T> switchIfEmpty(Publisher<? extends T> other) {
        ObjectHelper.requireNonNull(other, "other is null");
        return RxJavaPlugins.onAssembly(new FlowableSwitchIfEmpty<T>(this, other));
    }
Returns a Flowable that emits the items emitted by the source Publisher or the items of an alternate
Publisher if the source Publisher is empty.
<p>
<img width="640" height="255" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/switchifempty.png" alt="">
<dl>
<dt><b>Backpressure:</b></dt>
<dd>If the source {@code Publisher} is empty, the alternate {@code Publisher} is expected to honor backpressure.
If the source {@code Publisher} is non-empty, it is expected to honor backpressure as instead.
In either case, if violated, a {@code MissingBackpressureException} <em>may</em> get
signaled somewhere downstream.
</dd>
<dt><b>Scheduler:</b></dt>
<dd>{@code switchIfEmpty} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>

@param other
the alternate Publisher to subscribe to if the source does not emit any items
@return  a Publisher that emits the items emitted by the source Publisher or the items of an
alternate Publisher if the source Publisher is empty.
@since 1.1.0