src/main/java/io/reactivex/Observable.java
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Observable<T> mergeWith(@NonNull MaybeSource<? extends T> other) {
        ObjectHelper.requireNonNull(other, "other is null");
        return RxJavaPlugins.onAssembly(new ObservableMergeWithMaybe<T>(this, other));
    }
@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Observable<T> mergeWith(@NonNull MaybeSource<? extends T> other) {
        ObjectHelper.requireNonNull(other, "other is null");
        return RxJavaPlugins.onAssembly(new ObservableMergeWithMaybe<T>(this, other));
    }
Merges the sequence of items of this Observable with the success value of the other MaybeSource
or waits both to complete normally if the MaybeSource is empty.
<p>
<img width="640" height="380" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/merge.png" alt="">
<p>
The success value of the other {@code MaybeSource} can get interleaved at any point of this
{@code Observable} sequence.
<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code mergeWith} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>
<p>History: 2.1.10 - experimental
@param other the {@code MaybeSource} which provides a success value to merge with or completes
@return the new Observable instance
@since 2.2