[SOLVED]
So I did a config class, and registered it, and now I'm getting a NPE during loading a single player world.
This is the stacktrace provided in crash-reports
This is my config class
This is where I register the config
This is my en_us.json
More than likely it is something I am missing.
I found that this part under FMLCommonSetupEvent was the NPE issue, replacing it with my config register was the fix.
ModLoadingContext.get().registerConfig(ModConfig.Type.SERVER, null);