Default Profile does not defaults back if the profile is deleted in the Project window

Steps to reproduce:

1. Download attached project and open in Unity.
2. Go to the Default Profile section: Project Settings >> Graphics >> HDRP >> Default Profile.
3. Change the DefaultSettingsVolumeProfile to ExteriorVolumeProfile.
4. Once the Confirmation Window shows up, click on Yes.
5. Delete the ExteriorVolumeProfile in the Project window.
6. Observe the Error in the Console: "Invalid VolumeProfile to obtain DiffusionProfileSettings".
7. Observe the Default Profile field is "None".

Actual results: Error in the Console: "Invalid VolumeProfile to obtain DiffusionProfileSettings". Default Profile field is "None".

Expected results: No error. Default Profile should fall back to some default profile, because it can't be empty.

Reproducible with versions: 

6000.3.9f1, 6000.4.0b7, 6000.5.0a7,  6000.6.0a3

Tested on (OS): 

MacBook Pro (16-inch, 2021), CPU: Apple M1 Max, Memory: 64 GB, macOS Tahoe: 26.1