How to return either Uni<Object> or Uni<Void>? - vert.x

Question

#Route(...)
public Uni<?> call() {
return Uni.createFrom().voidItem();
}
throws a NullPointerException: Invalid value returned by Uni: null
However
#Route(...)
public Uni<Void> call() {
return Uni.createFrom().voidItem();
}
works perfectly fine and responds with HTTP 204
How do I manage to get either Uni<Void> or Uni<AnyObject> from the same method?
I need to return http 204 only in specific scenarios

Answer 1

You can't do that directly as the types are different.
I would recommend using RESTEasy Reactive and do:
#GET
public Uni<Response> call() {
Uni<AnyObject> uni = .... ;
return uni
.onItem().transform(res -> {
if (res == null) return Response.noContent().build();
return Response.ok(res).build();
});
}
By emitting a Response object, you can customize the response status.
Another solution if you want to keep using Reactive Routes is to not return a Uni, but get the RoutingContext as a parameter:
#Route(...)
public void call(RoutingContext rc) {
HttpServerResponse response = rc.response();
Uni<AnyObject> uni = .... ;
return uni
.subscribe().with(res -> {
if (res == null) response.setStatus(204).end();
else response.setStatus(200).end(res);
}, failure -> rc.fail(failure)); // will produce a 500.
}