@Nullable (jakarta.annotation & org.jspecify.annotations)

Apache Causeway' defaults for properties and parameters is that they are mandatory unless otherwise stated. Both the @jakarta.annotation.Nullable annotation and @org.jspecify.annotations.Nullable annotation are recognized by Apache Causeway for both properties and parameters as means to indicate that the property/parameter is not mandatory.

For example:

import jakarta.annotation.Nullable;

@Nullable
@Getter @Setter
private String name;

or:

import jakarta.annotation.Nullable;

public Customer updateName(
        @Nullable final String name) {
    setName(name);
    return this;
}

Apache Causeway does provide several other ways to specify optionality: using the @Property#optionality() / @Parameter#optionality() annotation. For properties, the optionality can also be inferred from the JPA @Column#nullable() attribute.

Metamodel validation during bootstrapping checks that there are no conflicting definitions of optionality.