How to reproduce:
1. Create a new URP project
2. Create a Forward Renderer(Create > Rendering > Universal Rendering Pipeline > Forward Renderer)
3. Select it in the Project window and add Render Objects to the list of Renderer Features
4. Remove NewRenderObjects from the list by selecting it and clicking the minus symbol
5. Undo this action(Edit > Undo Inspector)
6. Attempt to remove the restored 'None' list entry

Expected result: the undo action is unavailable as noted in the pop-up warning when removing an entry from the list or the restored list entry is removable
Actual result: the undo action is available thus contradicting the pop-up warning; the restored list entry cannot be removed and throws NullReferenceExceptions

Reproducible with: 2019.2.10f1, 2019.3.0b7, 2020.1.0a9
Could not test with: 2017.4.33f1, 2018.4.11f1(package versions with Forward Renderer implementation unavailable)

Reproducible with package versions: 5.10.0, 7.1.2
Could not test with package versions: 4.10.0(Forward Renderer not yet implemented), 5.7.2, 5.9.0(Forward Renderer features list not working)