Implementação do Filtro para NotaFiscal

Não consegui seguir a linha de raciocínio para implementar o filtro poderia me mostrar como ficaria.

package br.com.alura.processor;

import br.com.alura.model.NotaFiscal;

import java.util.concurrent.Flow;
import java.util.concurrent.SubmissionPublisher;

public class NotaFiscalFiltro extends SubmissionPublisher implements Flow.Processor {

    private Flow.Subscription subscription;

    @Override
    public void onSubscribe(Flow.Subscription subscription) {
        System.out.println("Chamando o onSubscribe");
        this.subscription = subscription;
    }

    @Override
    public void onNext(Object item) {
        NotaFiscal nf = (NotaFiscal)item;
        if(nf.getValor() > 0.0) {
            submit(nf);
        } else {
            System.out.println("Nota fiscal com o valor menor ou igual a zero");
        }
    }

    @Override
    public void onError(Throwable throwable) {
        throwable.printStackTrace();
    }

    @Override
    public void onComplete() {
        this.subscription.request(1);
    }
}

Fiz isso porem ele sempre para na primeira execução de uma nota fiscal

package br.com.alura;

import java.time.LocalDate;
import java.util.Scanner;
import java.util.concurrent.SubmissionPublisher;

import br.com.alura.model.NotaFiscal;
import br.com.alura.processor.NotaFiscalFiltro;
import br.com.alura.subscriber.NotaFiscalSubscriber;

public class TesteEnvioNaoBloqueante {

    public static void main(String[] args) {
        NotaFiscal primeiraNotaFiscal = new NotaFiscal("João", 39.99, LocalDate.now());
        NotaFiscal segundaNotaFiscal = new NotaFiscal("Renata", 39.99, LocalDate.now());
        NotaFiscal terceiraNotaFiscal = new NotaFiscal("Paulo", 39.99, LocalDate.now());
        SubmissionPublisher<NotaFiscal> publisher = new SubmissionPublisher<>();
        NotaFiscalFiltro filtro = new NotaFiscalFiltro();
        NotaFiscalSubscriber subscriber = new NotaFiscalSubscriber();

        publisher.subscribe(filtro);
        filtro.subscribe(subscriber);
        publisher.submit(primeiraNotaFiscal);
        publisher.submit(segundaNotaFiscal);
        publisher.submit(terceiraNotaFiscal);
        System.out.println("Você irá receber a nota fiscal no seu e-mail");

        Scanner scan = new Scanner(System.in);
        scan.nextLine();
        scan.close();

        publisher.close();
    }

}