What I expected to happen was...:
I wanted to visit the negative coordinates to see the new biomes, but when I arrived, instead of deepslate, there was only stone.

What actually happened was...:
I want to see deepslate, and there is only stones around me

Steps to Reproduce:
1. Create an map in 1.15.2
2. Update the map to the 21w44a
3. Dig to negative coordinates

4. Look around