Husky1017608 has null dutyDefToSubNode. Recovering by calling ResolveSubnodes() (though that should have been called already).
Verse.Log:Error(String)
RimWorld.ThinkNode_DutyConstant:TryIssueJobPackage(Pawn, JobIssueParams)
Verse.AI.ThinkNode_Priority:TryIssueJobPackage(Pawn, JobIssueParams)
RimWorld.ThinkNode_Conditional:TryIssueJobPackage(Pawn, JobIssueParams)
Verse.AI.ThinkNode_Priority:TryIssueJobPackage(Pawn, JobIssueParams)
Verse.AI.ThinkNode_Tagger:TryIssueJobPackage(Pawn, JobIssueParams)
Verse.AI.ThinkNode_Subtree:TryIssueJobPackage(Pawn, JobIssueParams)
Verse.AI.ThinkNode_Priority:TryIssueJobPackage(Pawn, JobIssueParams)
RimWorld.ThinkNode_Conditional:TryIssueJobPackage(Pawn, JobIssueParams)
Verse.AI.ThinkNode_Priority:TryIssueJobPackage(Pawn, JobIssueParams)
Verse.AI.Pawn_JobTracker:DetermineNextConstantThinkTreeJob()
Verse.AI.Pawn_JobTracker:DetermineNextJob(ThinkTreeDef&)
Verse.AI.Pawn_JobTracker:TryFindAndStartJob()
Verse.AI.Pawn_JobTracker:EndCurrentJob(JobCondition, Boolean)
RimWorld.Planet.CaravanFormingUtility:StartFormingCaravan(List`1, Faction, List`1, IntVec3, IntVec3, Int32)
RimWorld.Dialog_FormCaravan:TryFormAndSendCaravan()
RimWorld.Dialog_FormCaravan:<DoBottomButtons>m__565()
Verse.Dialog_MessageBox:DoWindowContents(Rect)
Verse.<WindowOnGUI>c__AnonStorey2C5:<>m__1B2(Int32)
UnityEngine.GUI:CallWindowDelegate(WindowFunction, Int32, GUISkin, Int32, Single, Single, GUIStyle)
Buy Husky from trader
Train Husky: Obedience Gold and Hauling Gold
Form Caravan
Include Husky
Husky causes red error
Error doesn't crash the game and Husky ended up still in the caravan.
Husky is still functioning fine after de-forming caravan
Thanks for reporting. It needs to be fixed. Though it doesn't seem to break the game so low priority for now.
Fixed for A18, thanks.