MissingReferenceException thrown continuously on selecting "Strip All ProBuilder Scripts in Scene" OR "Strip ProBuilder Script in Selection" Actions from the "Tools" menu when the "Smooth Group Editor" and "ProBuilder" window is docked, Refer attached video.

Steps to repro:
1. Create a new project.
2. Window > Package Manager > ProBuilder > Install
3. Tools > ProBuilder > ProBuilder Window
4. Shape Tools > Arch > Build
5. Tools > ProBuilder > Editors > Open Smoothing Editor > Dock
6. Tools > ProBuilder > Actions > Strip All ProBuilder Scripts in Scene

Actual Result:
MissingReferenceException thrown on "Strip All ProBuilder Scripts in Scene" action is performed with the "Smooth Group Editor" window docked in the editor

Expected Result:
"Strip All ProBuilder Scripts in Scene" OR "Strip ProBuilder Script in Selection" actions are performed gracefully

Occurring on:
2020.2.0a7, 2020.1.0b5, 2019.3.9f1, 2019.2.13f1, 2019.1.11f1, 2018.4.14f1, 2018.3.0f2, 2018.1.0f2

Package found version: preview.7 - 4.3.0, 4.2.3, 4.2.1, 4.1.0, 4.0.2, 3.0.0

Environment:
Windows10 and macOS 10.14

Stack trace:
MissingReferenceException: The object of type 'ProBuilderMesh' has been destroyed but you are still trying to access it.
Your script should either check if it is null or you should not destroy the object.
UnityEngine.Object.get_name () (at <148a27e5bcab4c229402b6d137ad62d9>:0)
UnityEditor.ProBuilder.SmoothGroupEditor.OnGUI () (at library/packagecache/com.unity.probuilder@4.3.0-preview.7/editor/editorcore/smoothgroupeditor.cs:539)
UnityEditor.HostView.InvokeOnGUI (UnityEngine.Rect onGUIPosition, UnityEngine.Rect viewRect) (at <b0707acaff7743ddbcba0f9c9b5c49cc>:0)
UnityEditor.DockArea.DrawView (UnityEngine.Rect viewRect, UnityEngine.Rect dockAreaRect) (at <b0707acaff7743ddbcba0f9c9b5c49cc>:0)
UnityEditor.DockArea.OldOnGUI () (at <b0707acaff7743ddbcba0f9c9b5c49cc>:0)
UnityEngine.UIElements.IMGUIContainer.DoOnGUI (UnityEngine.Event evt, UnityEngine.Matrix4x4 parentTransform, UnityEngine.Rect clippingRect, System.Boolean isComputingLayout, UnityEngine.Rect layoutSize, System.Action onGUIHandler, System.Boolean canAffectFocus) (at <bbbb88ae80ab4089bd1e62021a527f21>:0)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr, Boolean&)