Error while looting/mailing items on Classic WoW

[Angerreign]

I'm getting this error but I do not know why. I think I got it while mailing some greens to my enchanter character.

1x Plumber/Modules/LootUI_Main.lua:2031: attempt to call field 'GetItemStats' (a nil value)
[Plumber/Modules/LootUI_Main.lua]:2031: in function <Plumber/Modules/LootUI_Main.lua:2020>
[Plumber/Modules/LootUI_Main.lua]:575: in function 'SetItem'
[Plumber/Modules/LootUI_Main.lua]:516: in function 'SetData'
[Plumber/Modules/LootUI_Display.lua]:1628: in function 'OnErrored'
[Plumber/Modules/LootUI_Display.lua]:846: in function <Plumber/Modules/LootUI_Display.lua:829>
[C]: ?
[Plumber/Modules/LootUI_Display.lua]:616: in function 'OnLootOpened'
[Plumber/Modules/LootUI_Display.lua]:831: in function <Plumber/Modules/LootUI_Display.lua:829>

Locals:
data =

{
overflow = false
slotType = 1
classID = 2
link = "|cff1eff00|Hitem:25307::::::-15:402784278:70::::::::::|h[Shadow Dagger of Spirit]|h|r"
id = 25307
slotIndex = 1
looted = false
questType = 0
craftQuality = 0
quantity = 1
name = "Shadow Dagger of Spirit"
hideCount = true
locked = false
subclassID = 15
icon = 135641
quality = 2
}
(*temporary) = nil
(*temporary) = "|cff1eff00|Hitem:25307::::::-15:402784278:70::::::::::|h[Shadow Dagger of Spirit]|h|r"
(*temporary) = "attempt to call field 'GetItemStats' (a nil value)"
RareItems = {
224025 = true
}
ItemStatExclusion = {
251783 = "ITEM_MOD_CR_SPEED_SHORT"
262754 = "ITEM_MOD_CR_SPEED_SHORT"
}
TertiaryStats = {
1 = "ITEM_MOD_CR_LIFESTEAL_SHORT"
2 = "ITEM_MOD_CR_AVOIDANCE_SHORT"
3 = "ITEM_MOD_CR_SPEED_SHORT"
4 = "ITEM_MOD_CR_STURDINESS_SHORT"
}

[Peterodox]

Hi! I've recently added a feature to highlight equipment with tertiary stat bonuses for Retail, but sorry, I forgot to test it on Classic.

It'll be fixed in the next update, but before that happens, you will see this error whenever you loot an equippable item. You can manually fix it now by adding a pair of parentheses:

1. Open Interface\AddOns\Plumber\Modules\LootUI_Main.lua with any text editor.
2. Go to line #2029 or search data.classID == 2 or data.classID == 4 and data.link
3. Change the entire line to elseif (data.classID == 2 or data.classID == 4) and data.link and C_Item.GetItemStats then
4. Save the changes.

[Peterodox]

Hi! It's been fixed in our latest update.