function yo () 
          local u = nil 
          local u = {} 
          local u = getAccountData (getPlayerAccount(source), "cu") 
          for i,v in ipairs (u) do 
            addVehicleUpgrade (vehicle, v) 
          end 
        end 
addCommandHandler("upgrade", yo)  
 
ERROR: script\server.lua:5: bad argument #1 to 'ipairs' (table expected, got number) 
How can I fix it?