class Dispatcher {

    public static Object execute(String name, Object... args) {
        final Handler handler = ref.get().get(name);
        if (handler == null) {
            return DefaultHandler.INSTANCE.execute(args);
        } else {
            return handler.execute(args);
        }
    }

}

class DispatcherTest {

    @Test
    public void should_handle_default() {

        assertNull(Dispatcher.execute("x"));
    }

}