Unable to open forestry tab

[fisch24]

When clicking on the forestry tab nothing happens and the following error is produced. Other tabs work as intended.

Exception filling window for FluffyManager.MainTabWindow_Manager: System.NullReferenceException: Object reference not set to an instance of an object
  at FluffyManager.ManagerJob_Forestry.<RefreshAllowedTrees>b__42_3 (Verse.ThingDef td) [0x00008] in <c5fa71f27de04dae8575e358e626eac1>:0 
  at System.Linq.Enumerable+WhereEnumerableIterator`1[TSource].MoveNext () [0x00037] in <351e49e2a5bf4fd6beabb458ce2255f3>:0 
  at System.Linq.Enumerable+DistinctIterator`1[TSource].MoveNext () [0x0009a] in <351e49e2a5bf4fd6beabb458ce2255f3>:0 
  at System.Linq.Enumerable.Contains[TSource] (System.Collections.Generic.IEnumerable`1[T] source, TSource value, System.Collections.Generic.IEqualityComparer`1[T] comparer) [0x00036] in <351e49e2a5bf4fd6beabb458ce2255f3>:0 
  at System.Linq.Enumerable.Contains[TSource] (System.Collections.Generic.IEnumerable`1[T] source, TSource value) [0x0000a] in <351e49e2a5bf4fd6beabb458ce2255f3>:0 
  at FluffyManager.ManagerJob_Forestry.RefreshAllowedTrees () [0x000ed] in <c5fa71f27de04dae8575e358e626eac1>:0 
  at FluffyManager.ManagerTab_Forestry.Refresh () [0x0005e] in <c5fa71f27de04dae8575e358e626eac1>:0 
  at (wrapper dynamic-method) FluffyManager.ManagerTab_Forestry.FluffyManager.ManagerTab_Forestry.PreOpen_Patch1(FluffyManager.ManagerTab_Forestry)
  at FluffyManager.MainTabWindow_Manager.GoTo (FluffyManager.ManagerTab tab, FluffyManager.ManagerJob job) [0x0000b] in <c5fa71f27de04dae8575e358e626eac1>:0 
  at FluffyManager.MainTabWindow_Manager.DrawTabIcon (UnityEngine.Rect rect, FluffyManager.ManagerTab tab) [0x00050] in <c5fa71f27de04dae8575e358e626eac1>:0 
  at FluffyManager.MainTabWindow_Manager.DoWindowContents (UnityEngine.Rect canvas) [0x001d0] in <c5fa71f27de04dae8575e358e626eac1>:0 
  at Verse.Window.InnerWindowOnGUI (System.Int32 x) [0x00165] in <7927e938de4c4089b4add4215e58d5b1>:0 
Verse.Log:Error(String, Boolean)
Verse.Window:InnerWindowOnGUI(Int32)
UnityEngine.GUI:CallWindowDelegate(WindowFunction, Int32, Int32, GUISkin, Int32, Single, Single, GUIStyle)

Full output log:
https://gist.github.com/0cc9446b4487e470088d84881c600c8a