NullReferenceException is thrown when a Timeline Asset is created in a new folder after closing the Package Manager window with the Timeline package selected

How to reproduce:

1. Open the attached "IN-150223" project
2. In the top of the Unity editor, select “Window” > “Package Management” > “Package Manager”
3. In the “Package Manager” window, select any package other than “Timeline”
4. In the “Package Manager” window, select the "Timeline" package
5. Close the “Package Manager” window
6. In the Hierarchy tab, create an empty GameObject and keep it selected
7. In the top of the Unity editor, select “Window” > “Sequencing” > “Timeline”
8. In the Timeline window, click "Create"
9. In the appeared save dialog window, create a new folder and save the new file in it
10. Observe the Console

Actual result: “NullReferenceException: Object reference not set to an instance of an object” is thrown in the Console
Expected result: The Timeline Asset is created without any errors in the Console

Reproducible with: 1.8.8 (6000.2.0f1), 1.8.12 (6000.6.0a4 (77e2e2eea1be)), 6000.6.0b8, 6000.7.0a4
Not Reproducible with: 1.8.7 (6000.2.0f1)

Reproducible on: Windows 11 Enterprise (25H2)
Not reproducible on: No other environments tested

Notes: In older Unity editor versions (e.g. 6000.0.0b11) to open “Package Manager”, you just select “Window” > “Package Manager”