public Builder add(ItemType type, int qty) {
qty = qty < 0 ? 1 : qty;
inventory.add(
new Pair<>(type, qty <= type.getMaxStackQuantity() ? qty : type.getMaxStackQuantity()));
return this;
}
public Builder add(ItemType type) {
inventory.add(new Pair<>(type, type.getMaxStackQuantity()));
return this;
}