Describe the bug
Make sure to include:

1. What did you expect to happen? in craft tweaker i expected a code along the lines of mods.terrafirmacraft.ItemRegistry.registerFuel(immersiveengineering:material:6, 1800, 1500,true ,true); to work
2. What actually happened instead (i.e. what was the bug) the item registry threw an error that invalidated the script
3. If it was a crash, upload the full log file (latest.log)
4. If they would help to explain the issue, include screenshots
   

   TerraFirmaCraft/src/main/java/net/dries007/tfc/compat/crafttweaker/CTItemRegistry.java

   Line 263 in 181751c

   if (FuelManager.canRegister(fuel))

To Reproduce
Attention to detail is important!

1. Do '...' create a fuel registry in craft tweaker
2. Then do '...' load the game up

Meta Info

TerraFirmaCraft-MC1.12.2-0.29.0.115/current (after a restart and update)

• Were any other mods included? Can you reproduce it without these other mods? yes for the mods, and no
• If necessary, what other mods (including versions) MUST be present to experience the bug?
  Craft Tweaker, and a mod that adds an acceptable not already registered fuel source

The code checks if it can register the fuel, then throws an "already registered" error when it can. The if statement needs to be negated.