Currently (Spigot-1.12.2), calling Inventory.getStorageContents  _ (_instanceof AbstractHorseInventory) on Llama and all horse variant will return exactly the same as Inventory.getContents, including 2 "non-storage" slot.

In Vannila Minecraft, Horse have 2 "non-storage" slots, one for saddle, one for horse armor, but all other horse variant have only 1 "non-storage" slot for saddle. Llama otherwise have only 1 "non-storage" slot for carpet.

I think that there is some change should be made:

• getStorageContents for Llama and all horse variant shouldn't include that 2 "non-storage" slot.
• Llama Inventory should not be instanceof AbstractHorseInventory, only instanceof LlamaInventory.
• LlamaInventory should have 1 "non-storage" slot for carpet, have getDecor, setDecor but not getSaddle, setSaddle.