As you can see below upon starting up the game and logging in I always receive this error.

I can replicate this error every time I log in.
Below is the full error message.
Date: 2019-09-27 12:55:50
ID: 1
Error occured in: Global
Count: 1
Message: ...terface\AddOns\LunaUnitFrames\modules\reckstacks.lua line 56:
attempt to index field 'background' (a nil value)
Debug:
...terface\AddOns\LunaUnitFrames\modules\reckstacks.lua:56: ?()
LunaUnitFrames\LunaUnitFrames.lua:92: FireModuleEvent()
LunaUnitFrames\modules\layout.lua:123: Load()
LunaUnitFrames\modules\units.lua:282: CheckModules()
LunaUnitFrames\modules\units.lua:452:
LunaUnitFrames\modules\units.lua:351
[C]: SetAttribute()
LunaUnitFrames\modules\units.lua:792: LoadUnit()
LunaUnitFrames\modules\units.lua:1011: InitializeFrame()
LunaUnitFrames\LunaUnitFrames.lua:226: LoadUnits()
LunaUnitFrames\LunaUnitFrames.lua:40: OnInitialize()
LunaUnitFrames\LunaUnitFrames.lua:265:
LunaUnitFrames\LunaUnitFrames.lua:263
Locals:
self =

{
OnDisable = defined @interface\AddOns\LunaUnitFrames\modules\reckstacks.lua:44
moduleHasBar = true
OnCombatlog = defined @interface\AddOns\LunaUnitFrames\modules\reckstacks.lua:98
OnLayoutWidgets = defined @interface\AddOns\LunaUnitFrames\modules\reckstacks.lua:73
CheckTalents = defined @interface\AddOns\LunaUnitFrames\modules\reckstacks.lua:85
OnEnable = defined @interface\AddOns\LunaUnitFrames\modules\reckstacks.lua:7
OnLayoutApplied = defined @interface\AddOns\LunaUnitFrames\modules\reckstacks.lua:48
moduleKey = "reckStacks"
moduleName = "Reckoning Stacks"
Update = defined @interface\AddOns\LunaUnitFrames\modules\reckstacks.lua:113
}
frame = LUFUnitplayer {
0 =
OnLeave = defined @interface\AddOns\LunaUnitFrames\modules\units.lua:521
UnregisterAll = defined @interface\AddOns\LunaUnitFrames\modules\units.lua:137
reckStacks = {
}
auras = {
}
registeredEvents = {
}
UnitClassToken = defined @interface\AddOns\LunaUnitFrames\modules\units.lua:533
RegisterNormalEvent = defined @interface\AddOns\LunaUnitFrames\modules\units.lua:59
topFrameLevel = 5
RegisterUpdateFunc = defined @interface\AddOns\LunaUnitFrames\modules\units.lua:110
SetBlockColor = defined @interface\AddOns\LunaUnitFrames\modules\units.lua:183
unitType = "player"
SetRangeAlpha = defined @interface\AddOns\LunaUnitFrames\modules\units.lua:171
visibility = {
}
CheckModules = defined @interface\AddOns\LunaUnitFrames\modules\units.lua:239
indicators = {
}
unitInitialized = true
unitRealType = "player"
unit = "player"
ReregisterUnitEvents = defined @interface\AddOns\LunaUnitFrames\modules\units.lua:38
RegisterUnitEvent = defined @interface\AddOns\LunaUnitFrames\modules\units.lua:104
tagUpdate = {
}
fontstrings = {
}
UnregisterSingleEvent = defined @interface\AddOns\LunaUnitFrames\modules\units.lua:87
DisableRangeAlpha = defined @interface\AddOns\LunaUnitFrames\modules\units.lua:163
highFrame = {
}
fullUpdates = {
}
UnregisterUpdateFunc = defined @interface\AddOns\LunaUnitFrames\modules\units.lua:127
OnEnter = defined @interface\AddOns\LunaUnitFrames\modules\units.lua:507
BlizzRegisterUnitEvent = defined =[C]:-1
highlight = {
}
FullUpdate = defined @interface\AddOns\LunaUnitFrames\modules\units.lua:30
SetBarColor = defined @interface\AddOns\LunaUnitFrames\modules\units.lua:179
borders = {
}
}
reckStacks = {
0 =
blocks = {
}
fullSize = true
PixelSnapDisabled = true
}
(for index) = 1
(for limit) = 4
(for step) = 1
id = 1
texture = {
0 =
PixelSnapDisabled = true
}
(*temporary) = nil
(*temporary) = nil
(*temporary) =
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = "attempt to index field 'background' (a nil value)"