Getting the crafting result out of a custom crafting block

I have the following code in my container (which is a crafting mechanism):

    @Override
    public ItemStack slotClick(int index, int button, int mode, EntityPlayer player) {
        if (factory.isGhostOutputSlot(index)) {
            Slot slot = getSlot(index);
            if (slot.getHasStack()) {
                ItemStack result = slot.getStack().copy();
                getSlot(SLOT_BASE).decrStackSize(1);
                getSlot(SLOT_CONTROLLER).decrStackSize(1);
                getSlot(SLOT_TYPE_CONTROLLER).decrStackSize(1);
                getSlot(SLOT_ENERGY).decrStackSize(1);
                getSlot(SLOT_MEMORY).decrStackSize(1);
                getSlot(SLOT_ESSENCE).decrStackSize(1);
                slot.putStack(null);
                return result;
            } else {
                return null;
            }
        } else {
            return super.slotClick(index, button, mode, player);
        }
    }

The idea is that certain slots are consumed (this works) and that the crafted item is returned to the user. But apparently it just disappears. How can I make sure that the user can pull out the end result out of this crafter?