DBus newbie

[Adam Trhoň]

Hi, I am new to DBus technology and have a problem. A learn from
http://doc.trolltech.com/qq/qq20-dbus.html Here is my code:

class Animal : public QObject
{
	Q_OBJECT
    
	public:
	Animal() { mood = 0; }
    
	public slots:
	void feed(void) {
		++mood; 
		emit moodChanged(mood);
		return;
	}
	void shoutAt(void) {
		--mood;
		emit moodChanged(mood);
		return;
	}
    
	int currentMood() const { return mood; }

	signals:
	void moodChanged(int mood);
    
	private:
	int mood;
};

main.cpp file:
QDBusConnection bus = QDBusConnection::sessionBus();
bus.interface()->registerService("Farm");

Animal cat;

bus.registerObject("/animals/Dax", &cat, QDBusConnection::ExportAllSlots);

But when I try to feed my cat:
QDBusConnection::sessionBus().call(QDBusMessage::createMethodCall("Farm", "/animals/Dax", "", "feed"));

I get this error message:
process 18995: arguments to dbus_message_new_method_call() were incorrect, assertion "destination == NULL || _dbus_check_is_valid_bus_name (destination)" failed in file dbus-message.c line 1073.
This is normally a bug in some application using the D-Bus library.
QDBusConnection: error: could not send message to service "Farm" path "/animals/Dax" interface "" member "feed"

What is wrong? Thanks for any answers.