src/main/java/io/reactivex/Maybe.java
@CheckReturnValue
    @NonNull
    @SchedulerSupport(SchedulerSupport.NONE)
    public static <T> Maybe<T> fromRunnable(final Runnable run) {
        ObjectHelper.requireNonNull(run, "run is null");
        return RxJavaPlugins.onAssembly(new MaybeFromRunnable<T>(run));
    }
@CheckReturnValue
    @NonNull
    @SchedulerSupport(SchedulerSupport.NONE)
    public static <T> Maybe<T> fromRunnable(final Runnable run) {
        ObjectHelper.requireNonNull(run, "run is null");
        return RxJavaPlugins.onAssembly(new MaybeFromRunnable<T>(run));
    }
Returns a Maybe instance that runs the given Action for each subscriber and
emits either its exception or simply completes.
<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code fromRunnable} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>
@param <T> the target type
@param run the runnable to run for each subscriber
@return the new Maybe instance
@throws NullPointerException if run is null