ArgumentNullException thrown when reseting Adaptive Performance Settings with no reference set in Default Scaler settings

Steps to reproduce:

1. Create and open a new URP 3D project
2. Open Project Settings and Build Profiles windows
3. Create a Windows Profile in Build Profiles window and switch to it
4. Add the "Adaptive Performance Settings" setting
5. Expand Runtime Settings -> Scaler Profiles -> Default Scaler Profiler
6. Add a new Adaptive Performance Settings object field
7. Reset the "Adaptive Performance Settings" setting through the hamburger menu
8. Observe the Console

Actual results: A "ArgumentNullException: Value cannot be null." error is thrown

Expected results: Nothing is thrown

Reproducible with versions: 6000.3.14f1, 6000.4.5f1, 6000.5.0b6, 6000.6.0a3

Can’t test with versions: 5.1.6 (6000.0.73f1), 6000.4.4f1 (no "Reset" option until 6000.4.5f1)

Tested on (OS): Windows 11 Pro (25H2)

Notes:

• If a reference is set, the error will not be produced
• The "Adaptive Performance Settings" section breaks visually in Build Profiles window until it is disabled and re-enabled