@CheckReturnValue
    @NonNull
    @SchedulerSupport(SchedulerSupport.NONE)
    public static <T> Observable<T> error(Callable<? extends Throwable> errorSupplier) {
        ObjectHelper.requireNonNull(errorSupplier, "errorSupplier is null");
        return RxJavaPlugins.onAssembly(new ObservableError<T>(errorSupplier));
    }