Rimworld scenario editor error

Exception filling window for RimWorld.Page_ScenarioEditor: System.NullReferenceException: Object reference not set to an instance of an object
  at RimWorld.ScenPart_ThingCount.DoEditInterface (Verse.Listing_ScenEdit listing) [0x00191] in <81af9f8a18324e17b286924a43555a7c>:0
  at RimWorld.ScenarioUI.DrawScenarioEditInterface (UnityEngine.Rect rect, RimWorld.Scenario scen, UnityEngine.Vector2& infoScrollPosition) [0x0012e] in <81af9f8a18324e17b286924a43555a7c>:0
  at RimWorld.Page_ScenarioEditor.DoWindowContents (UnityEngine.Rect rect) [0x000a0] in <81af9f8a18324e17b286924a43555a7c>:0
  at Verse.Window.InnerWindowOnGUI (System.Int32 x) [0x001d3] in <81af9f8a18324e17b286924a43555a7c>:0
UnityEngine.StackTraceUtility:ExtractStackTrace ()
Verse.Log:Error (string)
Verse.Window:InnerWindowOnGUI (int)
UnityEngine.GUI:CallWindowDelegate (UnityEngine.GUI/WindowFunction,int,int,UnityEngine.GUISkin,int,single,single,UnityEngine.GUIStyle)