Currently you would not be able to catch an exception by calling StringLocalizer { key: null }. Suppose key should not be able to set to null.

var p2 = true;
try {
    var a2 = StringLocalizer { key: null };
    p2 = false;
}
catch (e2 : NullPointerException) {
}

System.out.println("test pass: {p2}");

I think it is better and easier o fix the issue at javafx.util.StringLocalilzer(choice a). Catch and rethrow the exception from there for being able to catch the exception from an application level.