Root level exception in OnGUI(): System.ArgumentNullException: Argument cannot be null.
Parameter name: type
  at System.Activator.CheckType (System.Type type) [0x00072] in /Users/builduser/buildslave/mono/build/mcs/class/corlib/System/Activator.cs:385
  at System.Activator.CreateInstance (System.Type type, Boolean nonPublic) [0x00000] in /Users/builduser/buildslave/mono/build/mcs/class/corlib/System/Activator.cs:343
  at System.Activator.CreateInstance (System.Type type) [0x00000] in /Users/builduser/buildslave/mono/build/mcs/class/corlib/System/Activator.cs:254
  at Verse.ThingMaker.MakeThing (Verse.ThingDef def, Verse.ThingDef stuff) [0x000c5] in C:\Dev\RimWorld\Assets\Scripts\Verse\Thing\ThingMaker.cs:44
  at RimWorld.Designator_Build.DesignateSingleCell (IntVec3 c) [0x00096] in C:\Dev\RimWorld\Assets\Scripts\RimWorld\UI\Designators\Place\Designator_Build.cs:284
  at Verse.DesignatorManager.ProcessInputEvents () [0x0006c] in C:\Dev\RimWorld\Assets\Scripts\Verse\UI\Designator\DesignatorManager.cs:71
  at RimWorld.MapInterface.HandleMapClicks () [0x0002d] in C:\Dev\RimWorld\Assets\Scripts\RimWorld\UI\MapInterface.cs:147
  at RimWorld.UIRoot_Play.UIRootOnGUI () [0x00176] in C:\Dev\RimWorld\Assets\Scripts\RimWorld\UI\UIRoot_Play.cs:105
  at Verse.Root.OnGUI () [0x0004f] in C:\Dev\RimWorld\Assets\Scripts\Verse\Global\Root\Root.cs:164
Verse.Log:Error(String, Boolean) (at C:\Dev\RimWorld\Assets\Scripts\Verse\Utility\Debug\Log\Log.cs:78)
Verse.Root:OnGUI() (at C:\Dev\RimWorld\Assets\Scripts\Verse\Global\Root\Root.cs:169)