WowAce

Hey, I'm trying to truncate player names to 6 characters in my Raid frames. I created a custom tag, but I don't know if it's the best way to accomplish my goal:

function(unit, unitOwner)
    return string.sub(UnitName(unitOwner), 1, 6)
end

This works fine when I use it for some frames, such as the Player frame. However, when I try to use it for Raid frames, I get the following Lua error:

Message: [string "return function(unit, unitOwner)..."]:2: bad argument #1 to 'sub' (string expected, got nil)
Time: Tue Jun 1 15:23:36 2021
Count: 1
Stack: [string "return function(unit, unitOwner)..."]:2: bad argument #1 to 'sub' (string expected, got nil)
[string "=(tail call)"]: ?
[string "=[C]"]: in function `sub'
[string "return function(unit, unitOwner)
return string.sub(UnitName(unitOwner), 1, 6)
end"]:2: in function `func'
[string "@Interface\AddOns\ShadowedUnitFrames\modules\tags.lua"]:232: in function `UpdateTags'
[string "@Interface\AddOns\ShadowedUnitFrames\modules\layout.lua"]:447: in function `InitFontString'
[string "@Interface\AddOns\ShadowedUnitFrames\modules\layout.lua"]:469: in function `SetupText'
[string "@Interface\AddOns\ShadowedUnitFrames\modules\layout.lua"]:144: in function `Load'
[string "@Interface\AddOns\ShadowedUnitFrames\modules\layout.lua"]:106: in function `Reload'
[string "@Interface\AddOns\ShadowedUF_Options\config.lua"]:219: in function <Interface\AddOns\ShadowedUF_Options\config.lua:213>
[string "@Interface\AddOns\ShadowedUF_Options\config.lua"]:1935: in function <Interface\AddOns\ShadowedUF_Options\config.lua:1877>
[string "=[C]"]: ?
[string "@Interface\AddOns\Ace3\AceConfig-3.0\AceConfigDialog-3.0\AceConfigDialog-3.0.lua"]:51: in function <...nfig-3.0\AceConfigDialog-3.0\AceConfigDialog-3.0.lua:49>
[string "@Interface\AddOns\Ace3\AceConfig-3.0\AceConfigDialog-3.0\AceConfigDialog-3.0.lua"]:847: in function <...nfig-3.0\AceConfigDialog-3.0\AceConfigDialog-3.0.lua:668>
[string "=[C]"]: ?
[string "@Interface\AddOns\Ace3\AceGUI-3.0\AceGUI-3.0.lua"]:72: in function <Interface\AddOns\Ace3\AceGUI-3.0\AceGUI-3.0.lua:70>
[string "@Interface\AddOns\Ace3\AceGUI-3.0\AceGUI-3.0.lua"]:306: in function `Fire'
[string "@Interface\AddOns\Ace3\AceGUI-3.0\widgets\AceGUIWidget-CheckBox.lua"]:68: in function <...ns\Ace3\AceGUI-3.0\widgets\AceGUIWidget-CheckBox.lua:57>

Locals: <none>

If I unlock frames at this point, then the addon gets very buggy. Some frames (Raid frames always, sometimes Party frames) appear in their unlocked states, even if I try to lock/unlock all frames. If I close the Options window, I can't re-open it with any of the slash commands. I guess there's something wrong with how I wrote the function, or with some way it interacts with Raid frames.