Version:
Mod -> tfmg-1.0.1b-1.21.1.jar
Neoforge -> 21.1.192

Exact error:
The game crashed: unexpected error
Error: java.lang.NullPointerException: Cannot invoke "java.lang.Integer.intValue()" because the return value of "net.minecraft.world.item.ItemStack.get(net.minecraft.core.component.DataComponentType)" is null

Steps to repeat error: (Done in creative)
Fill create copper tank with Lubrication Oil
Right click tank with Oil Can

Can replicate on tfmg 1.0.2f, create 6.0.6 and neoforge 21.1.197
crashes with steel fluid tanks too; I also believe the same bug happens with cooling fluid.