Root level exception in OnGUI(): System.ArgumentNullException: Value cannot be null.
Parameter name: type
at System.Activator.CreateInstance (System.Type type, System.Boolean nonPublic) [0x00003] in <eae584ce26bc40229c1b1aa476bfa589>:0
at System.Activator.CreateInstance (System.Type type) [0x00000] in <eae584ce26bc40229c1b1aa476bfa589>:0
at (wrapper dynamic-method) Verse.ThingMaker.Verse.ThingMaker.MakeThing_Patch1(Verse.ThingDef,Verse.ThingDef)
at Verse.DebugThingPlaceHelper.DebugSpawn (Verse.ThingDef def, Verse.IntVec3 c, System.Int32 stackCount, System.Boolean direct, Verse.ThingStyleDef thingStyleDef, System.Boolean canBeMinified, System.Nullable`1[T] wipeMode) [0x00013] in <8c412d4a16f94d4cb337e846f2dee469>:0
at Verse.DebugThingPlaceHelper+<>c__DisplayClass2_1.<TryPlaceOptionsForStackCount>b__1 () [0x0000b] in <8c412d4a16f94d4cb337e846f2dee469>:0
at Verse.DebugTool.DebugToolOnGUI () [0x00018] in <8c412d4a16f94d4cb337e846f2dee469>:0
at Verse.DebugTools.DebugToolsOnGUI () [0x00007] in <8c412d4a16f94d4cb337e846f2dee469>:0
at (wrapper dynamic-method) RimWorld.UIRoot_Play.RimWorld.UIRoot_Play.UIRootOnGUI_Patch2(RimWorld.UIRoot_Play)
at (wrapper dynamic-method) Verse.Root.Verse.Root.OnGUI_Patch2(Verse.Root)
UnityEngine.StackTraceUtility:ExtractStackTrace ()
Verse.Log:Error (string)
(wrapper dynamic-method) Verse.Root:Verse.Root.OnGUI_Patch2 (Verse.Root)

I get this error when trying to spawn a transport shuttle.