Steps to reproduce:

1. Set up perforce server and workspace
2. Add attached project to workspace
3. Open it using unity 2017.1.1f1 (or any other 2017.1, point is not to trigger API updater yet)
4. Enable VCS in project
5. Add "gameObject.light.color = Color.red" to HxVolumetricCamera.cs script's Start() and submit project to perforce server (if API updater pops up - cancel it for now)
6. Close and reopen project
7. When API updater window pops up - run updater.
8. Notice few unauthorized access exceptions and then NullReferenceException arising from compilation.

Note: you can skip adding "gameObject.light.color = Color.red" if you want to repro issue on 2018.1/2018.2 - project already has some code that will trigger API updater on those versions

Reproduced with: 2017.1.3p1, 2017.2.2f1, 2017.3.1p2, 2018.1.0.b9
Partially reproducible: 2018.2.0a3 (db66e9789be1)

By partially I mean that exceptions/loop will still be there until editor window is focused again - once editor is in focus window saying that scripts are recompiling will pop up and after couple of seconds exceptions will stop