Steps for reproduction:
1) Create an empty GameObject in Hierarchy
2) Create two cubes as a child of empty GameObject
3) Drag the GameObject to Project tab to convert it to a prefab
4) In Project tab, find the prefab and mark it as `Lightmap static` (or use any other static option) in Inspector tab
5) Say yes to setting all the child objects as static too
6) Crash or error thrown

Notes:
- (!) Bug only occurs on Mac platform, it's not reproducible on Windows
- Issue occurs on both debug/release modes
- Issue is introduced in 2018.1.0a1 (consistently reproduced in rev. 719f8569cac3)
- Crash issue is observed once