Authors CurseForge

Disclaimer: Brand new to writing WoW addons.

Basically trying to teach myself how to write addons, and the current task at hand is to cycle through all the items in my bags, and get the item level.

The problem I have is when I call "GetContainerItemID", it just returns nil for every combination of bag and slot, even though I expect at least 5 of those slots, not to return nil

local eventFrame = CreateFrame("FRAME");
eventFrame:RegisterEvent("BAG_UPDATE");

local function listBagItems ()
    for intBag=0,NUM_BAG_SLOTS do
        for intSlot=1, GetContainerNumSlots(intBag) do
            local intItem = GetContainerItemID(intBag, intSlot)
            print(intItem, intBag, intSlot)
        end
    end
end

local function eventHandler (self, event, arg)
    print ("Event Caught", event)
    if event == "BAG_UPDATE" then
        listBagItems()
    end    
end

eventFrame:SetScript("OnEvent", eventHandler);

Hopefully someone can point me in the right direction, or at least point out my mistake?

Tx in advance.