src/main/java/io/reactivex/Completable.java
@CheckReturnValue
    @SuppressWarnings("unchecked")
    @SchedulerSupport(SchedulerSupport.NONE)
    public final <T> Maybe<T> toMaybe() {
        if (this instanceof FuseToMaybe) {
            return ((FuseToMaybe<T>)this).fuseToMaybe();
        }
        return RxJavaPlugins.onAssembly(new MaybeFromCompletable<T>(this));
    }
@CheckReturnValue
    @SuppressWarnings("unchecked")
    @SchedulerSupport(SchedulerSupport.NONE)
    public final <T> Maybe<T> toMaybe() {
        if (this instanceof FuseToMaybe) {
            return ((FuseToMaybe<T>)this).fuseToMaybe();
        }
        return RxJavaPlugins.onAssembly(new MaybeFromCompletable<T>(this));
    }
Converts this Completable into a {@link Maybe}.
<p>
<img width="640" height="585" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Completable.toMaybe.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code toMaybe} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>

@param <T> the value type
@return a {@link Maybe} that only calls {@code onComplete} or {@code onError}, based on which one is
called by the source Completable.