Steps to repro:

1. Open attached project;
2. In the upper context menu choose Tools > Lightmaps > Bake Build Settings Scenes;
3. In the opened dialog window press 'Yes' button.

Expected result:
After some time scenes are baked successfully.

Actual result:
Editor freezes. The 'Lamp' scene seems to be the culprit.

Regression introduced in Unity 2018.1.0a4.

Notes:
- Reproduces in 2018.1.0a7, 2018.1.0a4;
- Not reproduces in 2018.1.0a3, 2017.3.0f2, 2017.2.1f1;
- Reproduces only for Enlighten; not reproduces for PLM;
- Also reproduces when baking active 'Lamp' scene, however, Editor doesn't freeze and the Lighting baking is stuck on Writing Lighting Data stage.