Console throws MissingReferenceException when user docks Tile Palette window in the editor, quits Unity and relaunches to create a new project.

Steps to reproduce:
1. Create > New Project
2. Window > Tile Palette
3. Dock Tile Palette Window anywhere
4. File > New Project...
5. Create new project or open any project

Observe that Missing Reference Exception is thrown on console.

Occuring with :
Unity 2018.2.0a7 , 2018.2.0a5 , 2018.2.0a4

Working with:
Unity 2018.2.0a3 , 2018.1.0b13 , 2017.3.0f3

Environment:
Occurring only on Windows 10 , Windows 7

Error Details:
MissingReferenceException: The object of type 'Camera' 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. UnityEditor.GridPaintPaletteClipboard.OnDisable () (at C:/buildslave/unity/build/Modules/TilemapEditor/Editor/Managed/Grid/GridPaintPaletteClipboard.cs:337) UnityEditor.GridPaintPaletteWindow:OnDisable()