Steps to reproduce:
1. Create new Unity project
2. In Project window create Blank Shader Graph
3. Open Shader Graph
4. In Blackboard create two Categories
5. In first Category add: Vector2 and Float Properties
6. In second Category add: Texture2D Property
7. Delete Categories
8. Press “+”
9. Try adding a new Property (Float or Vector2)

Actual results: Trying to add new Properties throws “NullReferenceException” error in the Console
Expected results: No warnings are thrown in the Console, user is able to add new Property

Reproducible with versions: 6000.0.67f1, 6000.3.9f1, 6000.4.0b9, 6000.5.0a7

Tested on (OS): macOS Silicon Tahoe 26.2 (M1)