Mule: Horse Armor in Inventory | But Slot is Missing in order to apply Horse Armor

1. In the horse's inventory, I should be able to view the "Armor Slot" next to the horse in order to apply the Horse Armor.

2. But the "Horse Armor Slot is Missing" next to horse. Only the saddle slot appears (1 slot).

3. The horse is tamed and I have a diamond horse armor in my Inventory.

Steps to Reproduce:
1. Click on horse inventory
2. Horse Armor appears in inventory
3. But no armor slot. Only saddle slot appears.

SCREENSHOT ATTACHED

Thank you.