lua – try to locally index the & # 39; items & # 39; (a null value)?

it's the code, and the error appears in this section, i do not know much about programming nor lua and i would like to ask for help as i can not find more information and have searched the internet to see how to fix it.

local function AddMapping (map, key, ...)
map[key] = {};
local elements = Utils.Pack (...);

for i = 1, items.n do - here I see the error
map[key][items[i]]= true;