How to reproduce:
1. Create a new project or open existing one
2. Locate Edit > Preferences > External Tools > External Script Editor
3. Choose Visual Studio as External Script Editor
4. Locate Edit > Project Settings > Editor > Script Compilation
5. Enable the experimental "MSBuild Compilation"
6. Wait for Editor to restart
7. Open Edit > Preferences > External Tools
8. Move cursor around External Tools window
9. Observe the Console
Actual result: "NullReferenceException" is logged from VisualStudioEditor.OnGUI every frame while cursor moves across the External Tools page, and the page fails to render
Expected result: The External Tools preferences render without errors
Reproducible with: 6000.7.0a3, 6000.7.0a6
Could not test with: 6000.0.83f1, 6000.3.23f1, 6000.6.1f1, 6000.7.0a2 (MSBuild Compilation not introduced yet)
Reproducible on: Windows 11 (25H2)
Not reproducible on: No other environments tested
Workaround: Disable the experimental MSBuild Compilation option, or select Rider as the external editor