Exception filling window for RimWorld.Dialog_Trade: System.NullReferenceException: Object reference not set to an instance of an object
  at Verse.Widgets.ThingIconWorker (UnityEngine.Rect rect, Verse.ThingDef thingDef, UnityEngine.Texture resolvedIcon, System.Single resolvedIconAngle, System.Single scale) [0x00000] in <acc1a8abfe07492884c6f18dcdaa4807>:0
  at Verse.Widgets.ThingIcon (UnityEngine.Rect rect, Verse.Thing thing, System.Single alpha, System.Nullable`1[T] rot) [0x00289] in <acc1a8abfe07492884c6f18dcdaa4807>:0
  at RimWorld.TransferableUIUtility.DrawTransferableInfo (RimWorld.Transferable trad, UnityEngine.Rect idRect, UnityEngine.Color labelColor) [0x00049] in <acc1a8abfe07492884c6f18dcdaa4807>:0
  at RimWorld.TradeUI.DrawTradeableRow (UnityEngine.Rect rect, RimWorld.Tradeable trad, System.Int32 index) [0x0030b] in <acc1a8abfe07492884c6f18dcdaa4807>:0
  at RimWorld.Dialog_Trade.FillMainRect (UnityEngine.Rect mainRect) [0x000c2] in <acc1a8abfe07492884c6f18dcdaa4807>:0
  at RimWorld.Dialog_Trade.DoWindowContents (UnityEngine.Rect inRect) [0x003d3] in <acc1a8abfe07492884c6f18dcdaa4807>:0
  at Verse.Window.InnerWindowOnGUI (System.Int32 x) [0x001ce] in <acc1a8abfe07492884c6f18dcdaa4807>:0
UnityEngine.StackTraceUtility:ExtractStackTrace ()
(wrapper dynamic-method) Verse.Log:Verse.Log.Error_Patch2 (string)
Verse.Window:InnerWindowOnGUI (int)
UnityEngine.GUI:CallWindowDelegate (UnityEngine.GUI/WindowFunction,int,int,UnityEngine.GUISkin,int,single,single,UnityEngine.GUIStyle)