"Unexpected sequence number on stored event." exception when dispatching an event from an @EventHandler method

[twerno]

When dispatching an Event inside EventHandler method the nested event is processed and added to the EventStore before the root event is.

import static org.axonframework.commandhandling.model.AggregateLifecycle.apply;

import org.axonframework.commandhandling.CommandHandler;
import org.axonframework.commandhandling.model.AggregateIdentifier;
import org.axonframework.eventsourcing.EventSourcingHandler;
import org.axonframework.test.aggregate.AggregateTestFixture;
import org.axonframework.test.aggregate.FixtureConfiguration;
import org.junit.Before;
import org.junit.Test;

import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.Value;

public class Example {
	
	private FixtureConfiguration<Aggregate> fixture;
	private final String ID = "id";
	
	@Before
	public void setUp() {
		fixture = new AggregateTestFixture<Aggregate>(Aggregate.class);
	}
	
	@Test
	public void testKontoUtworz() {
		fixture.givenNoPriorActivity()
			.when(new Command(ID))
			.expectEvents(new Event_1(ID), new Event_2(ID));
	}

}

@Value class Command {private String id;}
@Value class Event_1 {private String id;}
@Value class Event_2 {private String id; 
	public Event_2(String id) {
		this.id = id;
	}
}

@Data @NoArgsConstructor class Aggregate {
	
	@AggregateIdentifier
	private String id;
	
	@CommandHandler
	public Aggregate(Command command) {
		apply(new Event_1(command.getId()));
	}
	
	@EventSourcingHandler
	public void on(Event_1 event) {
		this.id = event.getId();
		apply(new Event_2(event.getId()));
	}
	
	@EventSourcingHandler
	public void on(Event_2 event) {}
}

Attached test finished with exception:

org.axonframework.eventsourcing.IncompatibleAggregateException: Aggregate identifier must be non-null after applying an event. Make sure the aggregate identifier is initialized at the latest when handling the creation event.

which direct cause is

Unexpected sequence number on stored event.

(The last exception is consumed silently due to default fixture configuration)