If you mean that literally [that nagarjuna does not mean to say anything about existence and non existence] then i do not understand. the commentaries on nagarjuna mention existence so many times!
Only to point repeatedly out that cognition of existence and non-existence are distortions, as far as I'm aware. He didn't speak in favour of it. (Again, happy to be corrected).
going back to the OP... it is true is it not that in theravada the doctrine of selflessness is just a conventional truth or "raft" that does not describe the goal [because nothing does] and which is to be abandoned when there. assuming that buddhas know reality, doesn't that mean that reality is not without a self?
Be a little careful not to be too loose with your distinctions here. In the original suttas, of which the Sutta Pitaka is one compilation thereof, the Buddha teaches the emptiness of all dhammas, but in the classical Theravada Abhidhamma tradition it is later believed that dhammas "exist" and "not exist" with great rapidity - billions in the blink of an eye, or somesuch. Classical Theravada came to regard sunnata as virtually synonymous as anatta, signifying merely that there was no self in any thing.
Live in concord, with mutual appreciation, without disputing, blending like milk and water, viewing each other with kindly eyesDhamma Wheel (Theravada forum)
* Here Comes Trouble