Unknown Error, how to fix?

So, expanding on my last question, I solved it, I accidentally added a false value, but I recently got a NEW error...

Workspace.TrelloAPI:547: attempt to concatenate local 'des' (a userdata value)

17:53:48.905 - Script 'Workspace.TrelloAPI', Line 547 - method AddCard

17:53:48.906 - Script 'Players.Player.PlayerGui.Application.Frame.create.Script', Line 16

Line 547:

desc=des.."",

Line 16:

 local CardID = ap:AddCard("[NS] " .. group.Name, id, ListID)

AddCard

function T:AddCard(...)
		local url
		local args={...}
		local dat
		if #args==3 then
			local nam,des,lid=args[1],args[2],args[3]
			dat={
			name=nam,
			desc=des.."",
			idList=lid,
			urlSource=nil,
			due=nil
			}
		elseif #args==4 then
			local nam,des,lid,url=args[1],args[2],args[3],args[4]
			dat={
			name=nam,
			desc=""..des,
			idList=lid,
			urlSource=url,
			due=nil
			}
		elseif #args==5 then
			local nam,des,lid,url,po=args[1],args[2],args[3],args[4],args[5]
			dat={
			name=nam,
			desc=""..des,
			idList=lid,
			urlSource=url,
			pos=po,
			due=nil
			}
		elseif #args==6 then
			local nam,des,lid,url,po,de=args[1],args[2],args[3],args[4],args[5],args[6]
			dat={
			name=nam,
			desc=""..des,
			idList=lid,
			urlSource=url,
			pos=po,
			due=de
			}
		elseif #args==7 then
			local nam,des,lid,url,po,de,label=args[1],args[2],args[3],args[4],args[5],args[6],args[7]
			dat={
			name=nam,
			desc=""..des,
			idList=lid,
			urlSource=url,
			pos=po,
			due=de,
			labels=label
			}
		elseif #args==8 then
			local nam,des,lid,url,po,de,label,cc=args[1],args[2],args[3],args[4],args[5],args[6],args[7],args[8]
			dat={
			name=nam,
			desc=""..des,
			idList=lid,
			urlSource=url,
			pos=po,
			due=de,
			labels=label,
			idCardSource=cc
			}
		end
	local data=HS:JSONEncode(dat)
	if Private then
			getAddon()
			url="https://api.trello.com/1/cards"..addon
		else
			 getAddon()
			 url="https://api.trello.com/1/cards"..addon
		end
		local re=HS:PostAsync(url,data)
		return HS:JSONDecode(re)
	end