Nagarjuna and the emptiness of the Dharma

Once Nagarjuna has demonstrated the emptiness of all exaggerated existential positions, including the existence of the Dharma and the Buddha's doctrine, how does he then affirm the validity of the Dharma? Is it because the Dharma teaches nothing other than its own emptiness (as well as the emptiness of everything) and thus is conventionally affirmed as the supreme teaching? Why does the Dharma hold a privileged position?