Description
As discussed in this forum thread:
http://apache-wicket.1842946.n4.nabble.com/INullAcceptingValidator-behavior-tp3570352p3570352.html
It appears that Wicket no longer calls INullAcceptingValidator intances when the validatable value is null.
Wicket wraps validators as behaviors, using the adapter pattern. The adapter class (org.apache.wicket.validation.ValidatorAdapter) implements the interface IValidator<T>. This "hides" the case where the actual validator is an INullAcceptingValidator. Therefore, when going through a component's attached validators, the code of org.apache.wicket.markup.html.form.FormComponent will never call INullAcceptingValidators when the value is null.