public void testIsNull() {
Item item1 = new PropertysetItem();
item1.addItemProperty("a", new ObjectProperty<String>(null,
String.class));
item1.addItemProperty("b",
new ObjectProperty<String>("b", String.class));
Item item2 = new PropertysetItem();
item2.addItemProperty("a",
new ObjectProperty<String>("a", String.class));
item2.addItemProperty("b", new ObjectProperty<String>(null,