src/main/java/io/reactivex/Maybe.java
@CheckReturnValue
    @NonNull
    @SchedulerSupport(SchedulerSupport.NONE)
    public final <R> Maybe<R> map(Function<? super T, ? extends R> mapper) {
        ObjectHelper.requireNonNull(mapper, "mapper is null");
        return RxJavaPlugins.onAssembly(new MaybeMap<T, R>(this, mapper));
    }
@CheckReturnValue
    @NonNull
    @SchedulerSupport(SchedulerSupport.NONE)
    public final <R> Maybe<R> map(Function<? super T, ? extends R> mapper) {
        ObjectHelper.requireNonNull(mapper, "mapper is null");
        return RxJavaPlugins.onAssembly(new MaybeMap<T, R>(this, mapper));
    }
Returns a Maybe that applies a specified function to the item emitted by the source Maybe and
emits the result of this function application.
<p>
<img width="640" height="515" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Maybe.map.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code map} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>

@param <R> the result value type
@param mapper
a function to apply to the item emitted by the Maybe
@return a Maybe that emits the item from the source Maybe, transformed by the specified function
@see <a href="http://reactivex.io/documentation/operators/map.html">ReactiveX operators documentation: Map</a>