How to reproduce:

1. Open HUB;
2. Create 3D(HDRP) project;
3. Create visual effect graph in the "Project" window (Create->Visual Effects-> Visual Effect Graph);
4. Drag it to the "Scene" window;
5. Select newly created graph in the "Project" window and go to "Inspector" window;
6. Click "Open" button;
7. In the opened graph window turn on "Blackboard";
8. Click "+" in it and select "Category";
9. Select added category and make a right click on it;
10. Select "Rename" function;
11. Delete default title, enter one space and click "Enter";
12. Select the same category and make a right click on it again;
13. Select "Duplicate".

Expected result: User should get validation message during category saving with the space instead of the title.
Actual result: Console displays error  "ArgumentNullException: Value cannot be null." 

Reproducible with: 12.1.7 (2021.3.12f1), 13.1.8 (2022.1.21f1),  14.0.3 (2022.2.0b12), 15.0.1 (2023.1.0a15).
Could not test with: 10.10.0 (2020.3.41f1), because "Duplicate" functionality not available on this stream.