Steps to reproduce the issue:
1. Download and open attached project.
2. Open scene named "Test".
3. In the "Hierarchy" window select game object named "GameObject".
4. In the "Inspector" window add component named "Script1".
5. Activate the "Debug" window.
6. Change the script target to "Script2".
7. Change the script target to "Script3".

Actual result:
The Editor crashes.

Expected result:
The Editor should not crash.

Reproduced with:
5.1.5f1, 5.2.5f1, 5.3.6f1, 5.3.6p1, 5.4.0f3, 5.5.0a4.

Note:
"Script1" has three serialized properties and OnDrawGizmos method.
"Script2" only has one serialized property and OnDrawGizmos method.
"Script3" has all three serialized properties but no OnDrawGizmos method.