I copy/paste the error code I'm recieving when using the "Outbreak" ability for unholy. AFAIK, the other abilities aren't having issues.

Below is the LUA error.

Message: Interface\AddOns\HeroLib\Class\Unit\Aura.lua:43: attempt to index local 'Spell' (a nil value)
Time: Wed Jul 18 19:15:16 2018
Count: 32
Stack: Interface\AddOns\HeroLib\Class\Unit\Aura.lua:43: attempt to index local 'Spell' (a nil value)
Interface\AddOns\HeroLib\Class\Unit\Aura.lua:43: in function Buff' Interface\AddOns\HeroLib\Class\Unit\Aura.lua:90: in function <Interface\AddOns\HeroLib\Class\Unit\Aura.lua:89> (tail call): ? Interface\AddOns\HeroRotation_DeathKnight\Unholy.lua:254: in function <Interface\AddOns\HeroRotation_DeathKnight\Unholy.lua:248> Interface\AddOns\HeroRotation_DeathKnight\Unholy.lua:267: in function <Interface\AddOns\HeroRotation_DeathKnight\Unholy.lua:263> Interface\AddOns\HeroRotation_DeathKnight\Unholy.lua:331: in function ?'
Interface\AddOns\HeroRotation\Main.lua:432: in function <Interface\AddOns\HeroRotation\Main.lua:410>

Locals: self =

{
AttackPowerDamageMod = defined @interface\AddOns\HeroLib\Class\Unit\Player\Stat.lua:61
RunicPowerDeficitPercentage = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:362
Race = defined @interface\AddOns\HeroLib\Class\Unit\Player\Main.lua:34
Insanityrain = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:599
FocusLossOnCastEnd = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:219
PainMax = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:668
IsInVehicle = defined @interface\AddOns\HeroLib\Class\Unit\Player\Main.lua:95
EnergyDeficit = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:257
Fury = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:645
InstanceInfo = defined @interface\AddOns\HeroLib\Class\Unit\Player\Instance.lua:68
RageDeficit = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:139
VersatilityDmgPct = defined @interface\AddOns\HeroLib\Class\Unit\Player\Stat.lua:98
ArcaneChargesDeficitPercentage = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:630
MaelstromPercentage = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:510
ArcaneCharges = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:615
ActiveMitigationNeeded = defined @interface\AddOns\HeroLib\Class\Unit\Player\Tank.lua:61
SoulShardsDeficit = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:427
IsInWhitelistedVehicle = defined @interface\AddOns\HeroLib\Class\Unit\Player\Main.lua:124
PainDeficit = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:686
AttackPower = defined @interface\AddOns\HeroLib\Class\Unit\Player\Stat.lua:57
ChiDeficit = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:544
PainDeficitPercentage = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:690
PrevOffGCD = defined @interface\AddOns\HeroLib\Events\Prev_Spell.lua:162
MasteryPct = defined @interface\AddOns\HeroLib\Class\Unit\Player\Stat.lua:93
InsanityPercentage = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:587
ManaDeficitPercentageP = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:105
FuryDeficit = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:656
PrevGCD = defined @interface\AddOns\HeroLib\Events\Prev_Spell.lua:140
AstralPowerMax = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:435
FocusDeficitPercentage = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:180
EnergyRegenPercentage = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:265
RunicPowerDeficit = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:358
FuryPercentage = defined @interface\Add

After reading into it a bit more, I think the error occurs due to Dark Arbiter being removed in BfA

Message: Interface\AddOns\HeroRotation_DeathKnight\Unholy.lua:275: attempt to index field 'DarkArbiter' (a nil value)
Time: Wed Jul 18 20:40:58 2018
Count: 212
Stack: Interface\AddOns\HeroRotation_DeathKnight\Unholy.lua:275: attempt to index field 'DarkArbiter' (a nil value)
Interface\AddOns\HeroRotation_DeathKnight\Unholy.lua:275: in function <Interface\AddOns\HeroRotation_DeathKnight\Unholy.lua:263>
Interface\AddOns\HeroRotation_DeathKnight\Unholy.lua:331: in function `?'
Interface\AddOns\HeroRotation\Main.lua:426: in function <Interface\AddOns\HeroRotation\Main.lua:410>

Locals: (*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = "attempt to index field 'DarkArbiter' (a nil value)"
HR =

{
MaxQueuedCasts = 3
CmdHandler = defined @interface\AddOns\HeroRotation\Core.lua:164
PulseInit = defined @interface\AddOns\HeroRotation\Main.lua:348
GetTexture = defined @interface\AddOns\HeroRotation\Core.lua:44
CastSuggested = defined @interface\AddOns\HeroRotation\Core.lua:153
CastAnnotated = defined @interface\AddOns\HeroRotation\Core.lua:104
PulsePreInit = defined @interface\AddOns\HeroRotation\Main.lua:294
LeftIconFrame = HeroRotation_LeftIconFrame {
}
MainFrame = HeroRotation_MainFrame {
}
GUISettings = {
}
AoEON = defined @interface\AddOns\HeroRotation\Core.lua:240
NameplateIconFrame = HeroRotation_NameplateIconFrame {
}
ToggleIconFrame = HeroRotation_ToggleIconFrame {
}
ChangePulseTimer = defined @interface\AddOns\HeroRotation\Main.lua:450
Commons = {
}
Print = defined @interface\AddOns\HeroRotation\Core.lua:31
ResetIcons = defined @interface\AddOns\HeroRotation\UI.lua:36
Cast = defined @interface\AddOns\HeroRotation\Core.lua:85
Nameplate = {
}
Pulse = defined @interface\AddOns\HeroRotation\Main.lua:410
Locked = defined @interface\AddOns\HeroRotation\Core.lua:250
Timer = {
}
CastLeftCommon = defined @interface\AddOns\HeroRotation\Core.lua:133
Ready = defined @interface\AddOns\HeroRotation\Main.lua:445
APLs = {
}
CastLeftOffset = 1
CreateBackdrop = defined @interface\AddOns\HeroRotation\UI.lua:61
CastQueue = defined @interface\AddOns\HeroRotation\Core.lua:115
SetAPL = defined @interface\AddOns\HeroRotation\Core.lua:37
SuggestedIconFrame = HeroRotation_SuggestedIconFrame {
}
CastLeftNameplate = defined @interface\AddOns\HeroRotation\Core.lua:144
SmallIconFrame = HeroRotation_SmallIconFrame {
}
MainIconFrame = HeroRotation_MainIconFrame {
}
CastSuggestedOffset = 1
CastLeft = defined @interface\AddOns\HeroRotation\Core.lua:138
MainIconPartOverlayFrame = HeroRotation_MainIconPartOverlayFrame {
}
CastOffGCDOffset = 1
GUI = {
}
ON = defined @interface\AddOns\HeroRotation\Core.lua:245
CDsON = defined @interface\AddOns\HeroRotation\Core.lua:235
}
I = {
ConvergenceofFates = {
}
InstructorsFourthLesson = {
}
ColdHeart = {
}
Taktheritrixs = {
}
}
Player = {
AttackPowerDamageMod = defined @interface\AddOns\HeroLib\Class\Unit\Player\Stat.lua:61
RunicPowerDeficitPercentage = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:362
Race = defined @interface\AddOns\HeroLib\Class\Unit\Player\Main.lua:34
Insanityrain = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:599
FocusLossOnCastEnd = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:219
PainMax = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:668
IsInVehicle = defined @interface\AddOns\HeroLib\Class\Unit\Player\Main.lua:95
EnergyDeficit = defined @interface\AddOns\HeroLib\Class\Unit\Player\Power.lua:257
Fury = defined