There was no stone generating near a lava pool in a savanna biome

What I expected to happen was:
Stone surrounding a lava pool with maybe a vein of coal or two

What actually happened was:
No stone at all, only grass and dirt blocks

Steps to Reproduce:
1. Seed: -314120316424971188
2. At coordinates: 156, 69, -200 there is a lava pool that generated without any stone