In the Enchantment table, it says no valid output for that item, even though there is nothing in the slot

In the Enchantment table, it says no valid output for that item, even though there is nothing in the slot in the Pocket UI.

How to reproduce:

1. Place an Enchantment Table
2. Open it
3. Press the Enchant button on the bottom of the screen.

Observed results: It says no valid output, even though there is no item in the slot.

Expected results: It should say nothing if there is no item in the slot.