How to handle null?

Learn how to execute specific actions on null items

The Uni type can emit null as item. While there are mixed feelings about null, it’s part of the Java language and so handled in the Uni type. Multi does not support null items as it would break the compatibility with Reactive Streams.

Emitting null is convenient when returning Uni<Void>. However, the downstream must expect null as item.

Thus, Uni provides specific methods to handle null item. uni.onItem().ifNull() lets you decide what you want to do when the received item is null:

uni.onItem().ifNull().continueWith("hello");
uni.onItem().ifNull().switchTo(() -> Uni.createFrom().item("hello"));
uni.onItem().ifNull().failWith(() -> new Exception("Boom!"));

A symmetric group of methods is also available with ifNotNull which let you handle the case where the item is not null:

uni
    .onItem().ifNotNull().transform(String::toUpperCase)
    .onItem().ifNull().continueWith("yolo!");

While supported, emitting null should be avoided except for Uni<Void>.