In Unity 2020.3.3 LTS whenever I try to open the wizard for adding object on the node like railings. It throwing a null exception. Not sure if anyone else has this issue. Tried debugging the GSD script but no luck. It work in 2021.2.xx Alpha version of Unity 3d.
Any help appreciated !

Error log
NullReferenceException: Object reference not set to an instance of an object
UnityEditor.ContainerWindow.FindUnsavedChanges (UnityEditor.View view) (at /home/bokken/buildslave/unity/build/Editor/Mono/ContainerWindow.cs:306)
UnityEditor.ContainerWindow.UnsavedStateChanged () (at /home/bokken/buildslave/unity/build/Editor/Mono/ContainerWindow.cs:329)
UnityEditor.EditorWindow.CreateNewWindowForEditorWindow (UnityEditor.EditorWindow window, System.Boolean loadPosition, System.Boolean showImmediately, System.Boolean setFocus) (at /home/bokken/buildslave/unity/build/Editor/Mono/EditorWindow.cs:1159)
UnityEditor.EditorWindow.Show (System.Boolean immediateDisplay) (at /home/bokken/buildslave/unity/build/Editor/Mono/EditorWindow.cs:614)
UnityEditor.EditorWindow.Show () (at /home/bokken/buildslave/unity/build/Editor/Mono/EditorWindow.cs:606)
UnityEditor.EditorWindow.GetWindowPrivate (System.Type t, System.Boolean utility, System.String title, System.Boolean focus) (at /home/bokken/buildslave/unity/build/Editor/Mono/EditorWindow.cs:658)
UnityEditor.EditorWindow.GetWindow (System.Type t) (at /home/bokken/buildslave/unity/build/Editor/Mono/EditorWindow.cs:690)
GSDSplineNEditor.DoExtAndEdgeOverview () (at Assets/RoadArchitect/Editor/GSDSplineNEditor.cs:617)
GSDSplineNEditor.OnInspectorGUI () (at Assets/RoadArchitect/Editor/GSDSplineNEditor.cs:463)
UnityEditor.UIElements.InspectorElement+<>c__DisplayClass59_0.b__0 () (at /home/bokken/buildslave/unity/build/External/MirroredPackageSources/com.unity.ui/Editor/Inspector/InspectorElement.cs:546)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr, Boolean&) (at /home/bokken/buildslave/unity/build/Modules/IMGUI/GUIUtility.cs:189)