ComponentEventBus implements Serializable { @SuppressWarnings("rawtypes") public boolean hasListener(Class<? extends ComponentEvent> eventType) { if (eventType == null) { throw new IllegalArgumentException("Event type cannot be null"); } return componentEventData.containsKey(eventType); } ComponentEventBus(Component component); Registration addListener(
            Class<T> eventType, ComponentEventListener<T> listener); Registration addListener(
            Class<T> eventType, ComponentEventListener<T> listener,
            Consumer<DomListenerRegistration> domListenerConsumer); @SuppressWarnings("rawtypes") boolean hasListener(Class<? extends ComponentEvent> eventType); @SuppressWarnings({ "unchecked", "rawtypes" }) void fireEvent(ComponentEvent event);  }
@Test(expected = IllegalArgumentException.class) public void hasListeners_nullEventType_throws() { new ComponentEventBus(new TestComponent()).hasListener(null); }