Execption on WorkTime()

[Aviuz]

https://gist.github.com/HugsLibRecordKeeper/66cbf6c020cabd5549aa82a7a4fa3a0e

Think I figured it out, kind of. It has something to do with Jecs vampires.
With the Work tab up, it shows an icon indicating what a prisoner is working on: wandering, idle, cutting stones, etc.
I have two vampires in prison, who refuse to work, and I'm quite certain did so in other colonies as well.
These vampires will swap their jobs from Idle to Wandering and do nothing else (aside from feeding on their cell mates now and then).
Everytime they do this, it throws a red error in the log.

I watched for a while to make sure. It's only the vampires causing that. No other prisoners will cause that when they swap work types.
I removed all available jobs from one vampire, and left the other as is, and they still would throw that error anytime they swapped from wandering to idle and back to wandering.

So is this something I should even be concerned about? Is it something that they'd have to fix on the Vampire end? It's not exactly ruining my game or anything.

Exception in Verse.AI.ThinkNode_Priority TryIssueJobPackage: System.NullReferenceException: Object reference not set to an instance of an object
  at PrisonLabor.PrisonLaborUtility.WorkTime (Verse.Pawn pawn) [0x00000] in <filename unknown>:0 
  at PrisonLabor.JobGiver_Labor.TryIssueJobPackage (Verse.Pawn pawn, JobIssueParams jobParams) [0x00000] in <filename unknown>:0 
  at Verse.AI.ThinkNode_Priority.TryIssueJobPackage (Verse.Pawn pawn, JobIssueParams jobParams) [0x00000] in <filename unknown>:0 
Verse.Log:Error(String, Boolean)
Verse.AI.ThinkNode_Priority:TryIssueJobPackage(Pawn, JobIssueParams)
Verse.AI.ThinkNode_Priority:TryIssueJobPackage(Pawn, JobIssueParams)
Verse.AI.ThinkNode_Conditional:TryIssueJobPackage(Pawn, JobIssueParams)
Verse.AI.ThinkNode_SubtreesByTag:TryIssueJobPackage(Pawn, JobIssueParams)
Verse.AI.ThinkNode_Priority:TryIssueJobPackage(Pawn, JobIssueParams)
Verse.AI.Pawn_JobTracker:DetermineNextJob_Patch5(Object, ThinkTreeDef&)
Verse.AI.Pawn_JobTracker:TryFindAndStartJob()
Verse.AI.Pawn_JobTracker:EndCurrentJob(JobCondition, Boolean)
Verse.AI.Pawn_JobTracker:JobTrackerTick()
Verse.Pawn:Tick_Patch1(Object)
Verse.TickList:Tick_Patch2(Object)
Verse.TickManager:DoSingleTick()
Verse.TickManager:TickManagerUpdate()
Verse.Game:UpdatePlay()
Verse.Root_Play:Update()