Iirc the event is from Wandering Caravans mod. The exception was thrown when the caravan spawned. I think it's due to pawn.apparel being null - since animals usually don't have it.

System.NullReferenceException: Object reference not set to an instance of an object
[Ref C3EDFF7A]
at Ammunition.Logic.AmmoLogic.CanBeLootedByColony (Verse.Thing thing) [0x0007f] in <6db39741cad546e388030636c00a10bb>:0
at Ammunition.Designators.Designator_LootAmmo.CanDesignateThing (Verse.Thing t) [0x00023] in <6db39741cad546e388030636c00a10bb>:0
at Verse.Designator.CreateReverseDesignationGizmo (Verse.Thing t) [0x00014] in <f0ac5eb9b52e4cc396c70fc9a4ee15e5>:0
at RimWorld.InspectGizmoGrid.DrawInspectGizmoGridFor (System.Collections.Generic.IEnumerable`1[T] selectedObjects, Verse.Gizmo& mouseoverGizmo) [0x0014a] in <f0ac5eb9b52e4cc396c70fc9a4ee15e5>:0 currentSelectable: null
UnityEngine.StackTraceUtility:ExtractStackTrace ()
(wrapper dynamic-method) MonoMod.Utils.DynamicMethodDefinition:Verse.Log.Error_Patch3 (string)
Verse.Log:ErrorOnce (string,int)
RimWorld.InspectGizmoGrid:DrawInspectGizmoGridFor (System.Collections.Generic.IEnumerable`1<object>,Verse.Gizmo&)
RimWorld.MainTabWindow_Inspect:DrawInspectGizmos ()
RimWorld.InspectPaneUtility:ExtraOnGUI (RimWorld.IInspectPane)
RimWorld.MainTabWindow_Inspect:ExtraOnGUI ()
Verse.WindowStack:WindowStackOnGUI ()
(wrapper dynamic-method) MonoMod.Utils.DynamicMethodDefinition:RimWorld.UIRoot_Play.UIRootOnGUI_Patch3 (RimWorld.UIRoot_Play)
(wrapper dynamic-method) MonoMod.Utils.DynamicMethodDefinition:Verse.Root.OnGUI_Patch2 (Verse.Root)