https://github.com/Ephys/TinkersSteelworks/blob/master/src/main/java/tsteelworks/common/core/TSContent.java#L178-L180
should be
https://github.com/SlimeKnights/TinkersConstruct/blob/master/src/main/java/tconstruct/world/TinkerWorld.java#L193

Also a check if they're null would be appropriate, in case the world module is disabled.

as there is no further input, I consider this issue closed

Are we sure we want to consider Oreberries as ores ? TiCon registered them as nuggets and TSteelworks added an "ore" entry to treat them as ores and output slag when they're smelted. I don't want to cause any problem with berries.

Also to be honest, I think the "should output slag" variable should be stored in the AdvancedSmelting entry instead of being based on the oredict names