Lua Whats the ID for nothing on item slot TFS 0.3.6 CD

[Misterion]

So, I've been trying to make a tile where only if the player has no item on his feet he can pass. I tried using the following function:

if getPlayerSlotItem(cid, 8) == 0 then

 

[Infernum]

 if getPlayerSlotItem(cid, CONST_SLOT_FEET).uid == 0 then