Heres the code this use to work on 1.7.10 but i think they changed the code. This is how i register the biome but the BiomeManager.warmBiomes has changed and i cant fix it.

 

biomeHellPlains = new BiomeHellPlains(50).setBiomeName("HellPlains");
	BiomeDictionary.registerBiomeType(biomeHellPlains, Type.WASTELAND);
	BiomeManager.warmBiomes.add(new BiomeEntry(biomeHellPlains, 10));

Here is what it should look like on the last line of your code:

BiomeManager.addBiomes(BiomeType.WARM, new BiomeEntry(biomeHellPlains, 10));

instead of

BiomeManager.warmBiomes.add(new BiomeEntry(biomeHellPlains, 10));

Thanks it worked.