Steps to repro:
1. Create the new HDRP project and open SampleScene;
2. In the Preferences window (Edit>Preferences) go to GI Cache tab;
3. Click Clean Cache button.

Expected result:
GI cache is cleared without errors in the Console.

Actual result:
Error:
"NullReferenceException: Object reference not set to an instance of an object
UnityEditor.PreferencesProvider.WriteRecentAppsList (System.String[] paths, System.String path, System.String prefsKey) (at <ca192453d8394227952a14f40675979e>:0)"
is shown. See attached video.

Notes:
- Reproducible in 2021.2.0b1, 2021.2.0a19;
- Not reproducible in Version 2021.2.0a18, 2021.1.13f1;
- Reproducible on Windows;
- Reproducible in HDRP; could not repro in built-in RP and URP.