Clean Selection in the SolutionExplorer Contextmenu throws Nullreference exception, when a unloaded project is selected

[Lohnegrim]

Describe the bug
Hi,
When I have a loaded and a unloaded project selected in the “Solution Explorer”-Window and select Cleanup in the Context Menu, then VS throws a NullReference.
The Error is reported here:
https://developercommunity.visualstudio.com/t/Clean-Selection-in-the-SolutionExplorer/10399038?viewtype=all

To Reproduce
Steps to reproduce the behavior:
1.) Create a new Solution with 2 projects
2.) Unload one project
3.) Select booth projects, richgclick on one of them and select 'Clean Selection'

Expected behavior
Clean of the selected and loaded excpetion

Screenshots

Additional context
As descriped in the Attached VS Community Report, when one of the projects is a VS-Installer Project, then it throws another error