SingleSubscribe

Single.java

    @SchedulerSupport(SchedulerSupport.NONE)
    @Override
    public final void subscribe(SingleObserver<? super T> subscriber) {
        ObjectHelper.requireNonNull(subscriber, "subscriber is null");

        subscriber = RxJavaPlugins.onSubscribe(this, subscriber);

        ObjectHelper.requireNonNull(subscriber, "subscriber returned by the RxJavaPlugins hook is null");

        try {
            subscribeActual(subscriber);
        } catch (NullPointerException ex) {
            throw ex;
        } catch (Throwable ex) {
            Exceptions.throwIfFatal(ex);
            NullPointerException npe = new NullPointerException("subscribeActual failed");
            npe.initCause(ex);
            throw npe;
        }
    }