How to reproduce:
1. Create a new project with a 3D template
2. Go to Package Manager (Window>Package Manager)
3. In the Package Manager press a plus sign on the top left side
4. Select "Add package from git URL"
5. Write: "com.unity.ai.navigation" and press enter

Expected result: No errors and Package Manager window is working
Actual result: The Package Manager window is blank and shows a button to sign in. Also, errors appear in the Console "NullReferenceException: Object reference not set to an instance of an object"

Reproducible with: 2021.2.0b10, 2021.2.0b12, 2022.1.0a6, 2022.1.0a8
Not reproducible with: 2019.4.30f1, 2020.3.18f1, 2021.1.20f1, 2021.2.0b9, 2022.1.0a5, 2022.1.0a9

Note:
- If you close the Package Manager window and try to open it again, it won't open
- You can open Package Manager if you close the project and open it again
- Package Manager window doesn't let you select AI Navigation
- Package Manager installs AI Navigation 1.0.0-exp.4