Method fromCallable

src/main/java/io/reactivex/rxjava3/core/Maybe.java:1079–1085

Returns a Maybe that invokes the given Callable for each individual MaybeObserver that subscribes and emits the resulting non-null item via onSuccess while considering a null result from the Callable as indication for valueless completion via {

(@NonNull Callable<? extends @Nullable T> callable)

     * @see #fromSupplier(Supplier)
     */
    @CheckReturnValue
    @NonNull
    @SchedulerSupport(SchedulerSupport.NONE)
    public static <T> Maybe<@NonNull T> fromCallable(@NonNull Callable<? extends @Nullable T> callable) {
        Objects.requireNonNull(callable, "callable is null");
        return RxJavaPlugins.onAssembly(new MaybeFromCallable<>(callable));
    }

    /**
     * Converts a {@link Future} into a {@code Maybe}, treating a {@code null} result as an indication of emptiness.