Installed Mods:
Thaumcraft BETA6
Railcraft 10.3.1

Launcher:
Twitch Client

Crashlog: https://pastebin.com/cceVCGUT

Seems to be related to Creosote potion, perhaps Thaumcraft is looking for a recipe that isn't there.

interesting!

@Azanor You should not assume that all the conversions are concrete classes.

Closing since azanor already fixed it in his code.

Nice