Output-channel of Service Activator

public class SimpleServiceActivatorWithOutput {

@ServiceActivator
public String sayHello(String name) {
return "Hello to " + name;
}
}


<int:channel id="output">
<int:queue/>
</int:channel>

<int:channel id="input"/>

<int:service-activator id="activator" ref="handler" input-channel="input" output-channel="output" />


@Test
public void test() {
input.send(MessageBuilder.withPayload("Jeff").build());
Message<?> r = output.receive();
System.out.println(r.getPayload());
}

If I replace SimpleServiceActivatorWithOutput with SimpleDelayedHandler:


public class SimpleDelayedHandler {

@ServiceActivator
public Object justDelay(Object obj) throws Exception {
int wait = new Random().nextInt(5);
System.out.println("Delays in thread " + Thread.currentThread().getId() + " for " + wait + " secs.");
TimeUnit.SECONDS.sleep(wait);
System.out.println("Ends Delaying in thread " + Thread.currentThread().getId());
return null;
}


I can't get things out of output-channel. But if I change "return null" to "return """, then everything works fine.