Describe the bug
Was flying in Bastion hovering over the location of the Valinor boss in Bastion (he had not respawned where I was) when I joined a world quest group to kill him. Immediately after phasing into the group I got the error below. Combat had not yet started.

Do you have an error log of what happened?

Message: Interface\AddOns\DBM-Core\DBM-Core.lua:11881: table index is nil
Time: Tue Jul 13 13:32:38 2021
Count: 1
Stack: Interface\AddOns\DBM-Core\DBM-Core.lua:11881: table index is nil
[string "@interface\AddOns\DBM-Core\DBM-Core.lua"]:11881: in function SetCreatureID' [string "@Interface\AddOns\DBM-Shadowlands\Morgeth.lua"]:5: in main chunk [string "=[C]"]: in function LoadAddOn'
[string "@interface\AddOns\DBM-Core\DBM-Core.lua"]:4358: in function LoadMod' [string "@Interface\AddOns\DBM-Core\DBM-Core.lua"]:4411: in function <Interface\AddOns\DBM-Core\DBM-Core.lua:4396> [string "@Interface\AddOns\DBM-Core\DBM-Core.lua"]:4422: in function handler'
[string "@interface\AddOns\DBM-Core\DBM-Core.lua"]:894: in function <Interface\AddOns\DBM-Core\DBM-Core.lua:881>

Locals: self =

{
timers = {
}
categorySort = {
}
instanceId = 1192
modelId = 98527
SyncThreshold = 8
modId = "DBM-Shadowlands"
zones = {
}
revision = 20210710161320
Options = {
}
DefaultOptions = {
}
iconRestore = {
}
addon = {
}
id = "2456"
specwarns = {
}
localization = {
}
announces = {
}
vb = {
}
optionCategories = {
}
}
cId = nil
(*temporary) = {
167524 = true
167526 = true
167525 = true
167527 = true
}
(*temporary) = 0
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = nil
(*temporary) = "table index is nil"
select = defined =[C]:-1
bossIds = {
167524 = true
167526 = true
167525 = true
167527 = true
}

Did you try having DeadlyBossMods as the only enabled addon and everything else (especially something like ElvUI) disabled?
No.

Which version of DeadlyBossMods are you using?
DBM-Core-9.1.3.zip installed 7/13/2021 using Overwolf
Was it working in a previous version? If yes, which was the last good one?
Yes. Not sure last time I did boss but haven't seen this error before.
Additional context