050_nullability.md

Nullability

With version 3.0.x of the OpenAPI specification one can declare a property to be nullable:

type: string
nullable: true

This plugin supports all possible combination of required/optional and nullable properties for serialisation (and deserialisation) and validation. Required properties which are nullable as well as optional properties which are not nullable are wrapped into a java.util.Optional. Optional properties which are nullable are wrapped into a special Tristate class to properly model all three states (value present, null or absent).

Required/Optional	Nullability	Getter return type
Required	Not Nullable	T
Required	Nullable	Optional<T>
Optional	Not Nullable	Optional<T>
Optional	Nullable	Tristate<T>

Tristate class

The special Tristate class is used for optional properties which are nullable. The Tristate class offers a compiler enforced chain of methods to handle all possible cases:

  String result = dto.getOptionalNullableProperty()
    .onValue(val -> "Value: " + val)
    .onNull(() -> "Property was null")
    .onAbsent(() -> "Property was absent");

The onValue method accepts a Function as argument, which gets the value as input. The onNull and onAbsent methods accepts a Supplier which gets executed in case the property was null or absent.