src/main/java/io/reactivex/Maybe.java
@CheckReturnValue
    @NonNull
    @SchedulerSupport(SchedulerSupport.NONE)
    public static <T> Maybe<T> error(Throwable exception) {
        ObjectHelper.requireNonNull(exception, "exception is null");
        return RxJavaPlugins.onAssembly(new MaybeError<T>(exception));
    }
@CheckReturnValue
    @NonNull
    @SchedulerSupport(SchedulerSupport.NONE)
    public static <T> Maybe<T> error(Throwable exception) {
        ObjectHelper.requireNonNull(exception, "exception is null");
        return RxJavaPlugins.onAssembly(new MaybeError<T>(exception));
    }
Returns a Maybe that invokes a subscriber's {@link MaybeObserver#onError onError} method when the
subscriber subscribes to it.
<p>
<img width="640" height="447" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Maybe.error.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code error} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>

@param exception
the particular Throwable to pass to {@link MaybeObserver#onError onError}
@param <T>
the type of the item (ostensibly) emitted by the Maybe
@return a Maybe that invokes the subscriber's {@link MaybeObserver#onError onError} method when
the subscriber subscribes to it
@see <a href="http://reactivex.io/documentation/operators/empty-never-throw.html">ReactiveX operators documentation: Throw</a>