Is the emptiness of final nirvana an illusion?

Is the emptiness of final nirvana an illusion? ------------------------------------------- When we misplace a box with nothing at all inside we haven't really lost its contents. I am convinced, based on this, *nothingness is only really inside things that exist*. Meaning at final nirvana, the conventional self, which *really no longer consists of anything at all*, is *really composed of absolutely nothing*, must **exist and have no parts**. Final nirvana does still arise, but the Buddha continues to exist, so emptiness, partite lack of substance, is an illusion. I'd like a Buddhist wide quote with sound reasoning.