How is Nagarjunas 'Shunyata' different from Buddhas 'Anatta'?

I am studying Nagarjuna's work online and from the commentaries understand that in the Madhyamika Nagarjuna describe 'Shunayata' as > all phenomena are conditional and empty of any self essence I am not able to understand how is this any different than the doctrine of Anatta that the Buddha taught? > that no unchanging, permanent self or essence can be found in any phenomenon.