Retained messages aren't pushed to the listener about hivemq-mqtt-client

[andsel]

I think I've found an issue that could be related to this:

@Test
    public void test() throws Exception {
        final Mqtt5BlockingClient publisher = com.hivemq.client.mqtt.MqttClient.builder()
            .useMqttVersion5()
            .identifier("publisher")
            .serverHost("localhost")
            .serverPort(1883)
            .buildBlocking();
        Mqtt5Connect connectRequest = Mqtt5Connect.builder()
            .cleanStart(true)
            .build();
        assertEquals(Mqtt5ConnAckReasonCode.SUCCESS, publisher.connect(connectRequest).getReasonCode(), "publisher" + " connected");
        //publish a retained message
        publisher.publishWith()
            .topic("metric/temperature/living")
            .payload("18".getBytes(StandardCharsets.UTF_8))
            .retain(true)
            .qos(MqttQos.AT_LEAST_ONCE)
            .send();

        // receive retained only if new subscription
        final Mqtt5BlockingClient subscriber = com.hivemq.client.mqtt.MqttClient.builder()
            .useMqttVersion5()
            .identifier("subscriber")
            .serverHost("localhost")
            .serverPort(1883)
            .buildBlocking();
        assertEquals(Mqtt5ConnAckReasonCode.SUCCESS, subscriber.connect().getReasonCode(), "subscriber" + " connected");
        subscriber.subscribeWith()
            .topicFilter("metric/temperature/living")
            .qos(MqttQos.AT_LEAST_ONCE)
            .retainHandling(Mqtt5RetainHandling.SEND_IF_SUBSCRIPTION_DOES_NOT_EXIST)
            .send();

        try (Mqtt5BlockingClient.Mqtt5Publishes publishes = subscriber.publishes(MqttGlobalPublishFilter.ALL)) {
            Optional<Mqtt5Publish> publishMessage = publishes.receive(1, TimeUnit.SECONDS);
            if (!publishMessage.isPresent()) {
                fail("Expected to receive a publish message");
                return;
            }
            Mqtt5Publish pub = publishMessage.get();
            assertEquals("18", new String(pub.getPayloadAsBytes(), StandardCharsets.UTF_8));
        }
    }