### Question:
StateHandler extends FeatureModel implements Updatable, Recyclable, Listenable<StateTransitionListener> { public void changeState(Class<? extends State> next) { Check.notNull(next); this.next = next; } StateHandler(Services services, Setup setup); @SuppressWarnings("unchecked")  StateHandler(Services services, Setup setup, Function<Class<? extends State>, String> converter); void changeState(Class<? extends State> next); boolean isState(Class<? extends State> state); void postUpdate(); @Override void addListener(StateTransitionListener listener); @Override void removeListener(StateTransitionListener listener); @Override void update(double extrp); @Override void recycle();  }### Answer:
@Test void testNullArgument() { final StateHandler handler = new StateHandler(services, setup); assertThrows(() -> handler.changeState(null), "Unexpected null argument !"); }