Help with player inventory

I made this program that should store players items and place them into a grave when they die. For some reason when it checks the inventory, no matter what slot, always find 0 air and i dont know what im doin bad. Pls help https://mega.nz/file/PfR1xaAL#tj3WSq1J6aTp4f3uvgWzjCL0b25-mvLyqzlror0UxzU