Simple oregen datapack failing to load

(As a few of you will have seen, I was trying to change modded ore generation. I have simplified things to only vanilla, and it is still not working). Basically, all I am attempting to do is generate nether gold ore in the plains biome, to test my understanding of datapacks. Hopefully this will help me with my other datapack, since I seem to be having the same problem here. Any time I add any line to the biome file, it fails to load a world.