The callback is called with newValue being null When registering a callback using RegisterValueChangeCallback in EnumField

How to reproduce:
1. Open the attached project "IN-70385.zip"
2. Open Assets/Scenes/SampleScene.unity
3. Select "GameObject" in the Hierarchy window
4. Drag and Drop Assets/TestMonoBehaviour.cs from the Project window onto the "GameObject" in the Hierarchy window

Expected results: "new value ? A" is printed in the Console window
Actual results: "new value ? null" is printed in the Console window

Reproducible with: 2021.3.36f1, 2022.3.21f1, 2023.2.14f1, 2023.3.0b10

Reproducible on: Windows 11 22H2
Not reproducible on: No other environment tested