Editor throws NullReferenceException on entering in play mode when Sikking editor or Custom Outline OR Custom Physics Shape module is selected and Sprite Editor window is docked and undocked earlier. refer attached video.

Steps to repro:
1. Create a new project
2. Import any .png in the project
3. Inspector > Sprite Editor
4. Dock and undock "Sprite Editor" window
4. Select Skinning Editor OR Custom Outline OR Custom Physics Shape
5. Hit play

Actual Result:
NullReferenceException thrown when "Skinning Editor OR Custom Outline OR Custom Physics Shape" module is selected and entered in Play mode with Sprite Editor window docked and undocked earlier.

Expected Result:
Editor enters in play mode without throwing any exception

Occurring on:
2020.2.0a1, 2020.1.0a25

Working Fine on:
2020.1.0a24, 2019.3.3f1

Environment:
Windows 10 and macOS 10.14

Stack trace:
Skinning Editor:
NullReferenceException: Object reference not set to an instance of an object
UnityEditor.UIElements.DefaultWindowBackend.OnEventsInterestsChanged () (at <e859a479319a4a5a8d9711977e98d28e>:0)
UnityEditor.GUIView.set_eventInterests (UnityEngine.EventInterests value) (at <e859a479319a4a5a8d9711977e98d28e>:0)
UnityEditor.EditorWindow.MakeParentsSettingsMatchMe () (at <e859a479319a4a5a8d9711977e98d28e>:0)
UnityEditor.EditorWindow.set_wantsMouseMove (System.Boolean value) (at <e859a479319a4a5a8d9711977e98d28e>:0)
UnityEditor.U2D.Sprites.SpriteEditorWindow.set_enableMouseMoveEvent (System.Boolean value) (at F:/build1/2020.2.0a1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.2d.sprite/Editor/SpriteEditor/SpriteEditorWindow.cs:1099)
UnityEditor.U2D.Animation.SkinningModule.OnModuleDeactivate () (at Library/PackageCache/com.unity.2d.animation@4.1.1/Editor/SkinningModule/SkinningModule.cs:129)
UnityEditor.U2D.Sprites.SpriteEditorWindow.OnDisable () (at F:/build1/2020.2.0a1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.2d.sprite/Editor/SpriteEditor/SpriteEditorWindow.cs:541)

Custom Outline:
NullReferenceException: Object reference not set to an instance of an object
UnityEditor.UIElements.DefaultWindowBackend.OnEventsInterestsChanged () (at <e859a479319a4a5a8d9711977e98d28e>:0)
UnityEditor.GUIView.set_eventInterests (UnityEngine.EventInterests value) (at <e859a479319a4a5a8d9711977e98d28e>:0)
UnityEditor.EditorWindow.MakeParentsSettingsMatchMe () (at <e859a479319a4a5a8d9711977e98d28e>:0)
UnityEditor.EditorWindow.set_wantsMouseMove (System.Boolean value) (at <e859a479319a4a5a8d9711977e98d28e>:0)
UnityEditor.U2D.Sprites.SpriteEditorWindow.set_enableMouseMoveEvent (System.Boolean value) (at F:/build1/2020.2.0a1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.2d.sprite/Editor/SpriteEditor/SpriteEditorWindow.cs:1099)
UnityEditor.U2D.Sprites.SpriteOutlineModule.OnModuleDeactivate () (at F:/build1/2020.2.0a1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.2d.sprite/Editor/SpriteEditorModule/SpriteOutlineModule.cs:377)
UnityEditor.U2D.Sprites.SpriteEditorWindow.OnDisable () (at F:/build1/2020.2.0a1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.2d.sprite/Editor/SpriteEditor/SpriteEditorWindow.cs:541)