This here works fine:

import mods.modularmachinery.RecipePrimer;
val copperfondery = mods.modularmachinery.RecipeBuilder.newBuilder("copperfondery", "fondry", 100, 0);

copperfondery.addItemInput(embers:ore_copper);
copperfondery.addItemOutput(embers:ingot_copper);
copperfondery.addItemOutput(embers:nugget_copper * 4);
copperfondery.build();

This cause a crash:

import mods.modularmachinery.RecipePrimer;
val tinfondery = mods.modularmachinery.RecipeBuilder.newBuilder("tinfondery", "fondry", 100, 0);

tinfondery.addFuelItemInout(200);
tinfondery.addItemInput(embers:ore_tin);
tinfondery.addItemOutput(embers:ingot_tin);
tinfondery.addItemOutput(embers:nugget_tin * 4);
tinfondery.build();

Also tested it with:
tinfondery.addFuelItem"Input"(200);