Was running Heroic 25 ICC on my Paladin and received this error after starting the Lich King encounter and mousing over/selecting him before combat started. Thanks.

Date: 2019-08-31 23:42:40
ID: 12
Error occured in: Global
Count: 1
Message: ..\AddOns\AllTheThings\AllTheThings.lua line 6170:
attempt to concatenate a nil value
Debug:
(tail call): ?
[C]: ?
AllTheThings\AllTheThings.lua:6170:
AllTheThings\AllTheThings.lua:6141
AllTheThings\AllTheThings.lua:2093:
AllTheThings\AllTheThings.lua:2027
AllTheThings\AllTheThings.lua:3580:
AllTheThings\AllTheThings.lua:3579
AllTheThings\AllTheThings.lua:3645:
AllTheThings\AllTheThings.lua:3582
[C]: ?
...ce\AddOns\AchieveIt\libs\AceHook-3.0\AceHook-3.0.lua:95:
...ce\AddOns\AchieveIt\libs\AceHook-3.0\AceHook-3.0.lua:87
[C]: ?
[C]: ?
[C]: ?
[C]: ?
[C]: ?
[C]: ?
Locals:
(*temporary) = defined =[C]:-1

AddOns:

Are you using the latest GIT build or the release version 1.9.8? Just ran through ICC but was unable to reproduce this.

I am using the latest 1.9.8, Possibly a fluke if it didn't happen for you. I'm going to be running another character through later so I'll see if it occurs again.

I did identify a possible race condition in Selfie Filters whereby description text could cause a similar error to what you were experiencing due to a slow response from GetItemInfo() in blizzard's API. Once your client caches the item name, the error should no longer occur.

A fix was made in commit 3aa0b97 and will be pushed out with the next release.