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 click "Blackboard" button;
8. On the opened "Blackboard" window make right mouse click.

Expected result: Nothing should happen, because window is empty.
Actual result: Menu with two options - "Select All" and "Select Unused"  becomes available.

Reproducible with: 10.10.0 (2020.3.41f1), 12.1.7 (2021.3.12f1), 13.1.8 (2022.1.21f1),  14.0.3 (2022.2.0b12), 15.0.1 (2023.1.0a16).