... The Death Note doesn't say any of that. Ryuk said that bit about neither heaven nor hell way back near the beginning (Timeline wise at least. Plot wise I believe it first appeared in that last chapter, though I don't recall exactly.). The nothingness is where ALL humans go after they die in that series. The irony is that Light, who thought himself like a god who passed judgement on the sinful was worth exactly the same after his death as those he thought of as trash and cleansed during his life. Unless they changed the Anime beyond that whole bit about getting rid of Light begging for his life at the end, I don't see where the confusion is coming from.