How to reproduce:
1. Open the attached “IN-142905_toggle” project
2. Open the “SampleScene” Scene
3. In the Hierarchy window, create a Toggle or a Slider GameObject
4. Select the created Toggle or Slider GameObject
5. In the Inspector window, make sure that Transition is set to either “Color Tint” or “Sprite Swap”
6. Set the Target Graphic to None
7. Try to set the Target Graphic to any other value other than None
8. Observe the Console window

Actual result: A NullReferenceException error is thrown, and the Target Graphics value is still set to None
Expected result: The Target Graphics value is successfully changed to the chosen value

Reproducible with: 6000.4.7f1, 6000.5.0b8, 6000.6.0a1 (7dc703ab9bd8), 6000.6.0a5
Not reproducible with: 6000.0.75f1, 6000.3.15f1, 6000.5.0a7

Reproducible on: Windows 11, Devuan GNU/Linux 6 (excalibur) (6.12.86) (by user)
Not reproducible on: No other environments tested

Notes:
- After setting the Toggle GameObject's value to None, you are no longer able to set it to any different value even after a Domain Reload or a project restart
- Custom classes that derive from Toggle are broken, because the Target Graphic in those cases is set to None by default