Create Node popup remains and a "NullReferenceException" error is thrown when the Create node popup is opened and the Project is reopened

Steps to reproduce:

1. Create a new Unity project using the Universal 3D template
2. Install the Visual Effect Graph package (com.unity.visualeffectgraph)
3. Create a new Visual Effect Graph (Assets > Visual Effects > Visual Effect Graph)
4. Double click the Visual Effect Graph to open the Visual Effect Graph window
5. Open the Create node popup (Right click > Create Node)
6. Close the Editor
7. Reopen the project
8. Observe the Editor

Actual results: The Create node popup is still showing and a "NullReferenceException: Object reference not set to an instance of an object" error is thrown with "Cannot save invalid window " warnings

Expected results: No errors or warnings and there is no Create node popup

Reproducible with versions: 6000.1.0a3, 6000.1.16f1, 6000.2.0f1, 6000.3.0a4

Not reproducible with versions: 6000.0.55f1, 6000.1.0a2

Tested on (OS): macOS Silicon Sequoia 15.5