setspecialdescription error

[Coca Cola]

how can i fix ?
obs : can't change to doitemsetattribute(uid, "description", param) because i need this to be a specialdescription


and i need dosetitemspecialdescription(uid, desc) functions in lib pls

ty,cya

function onSay(cid, words, param, channel)
 if(desc == "") then
 doPlayerSendCancel(cid, "You have to type a special description.")
 return true 
end 
local pos = getCreatureLookPosition(cid)
 pos.stackpos = STACKPOS_TOP_MOVEABLE_ITEM_OR_CREATURE 
local item = getThingFromPos(pos).uid
if(item) then doSetItemSpecialDescription(item, desc) 
end 
return true
end