@Nullable (javax.validation)

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

For example:

@javax.annotation.Nullable
public String getName() {
    return name;
}
public void setName(final String name) {
    this.name = name;
}

or:

public Customer updateName(@javax.annotation.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 @Column#allowsNull() attribute.

If more than one method is specified then the framework will validate that there are no incompatibilities (and fail to boot otherwise).