To reproduce:
1. Open project attached by the user
2. Open "test" scene
3. Make sure that auto generate is disabled in lightning window and that cube is marked as lightmap static
4. Move game object "cube"
5. Undo ( ctrl + z)
6. Notice error in console

Expected: Undoing done without errors
Actual: Errors in console every time ctrl+z is pressed.

Reproduced with: 5.6.0f3, 5.6.0p3, 2017.1.0b3
Not reproducible with : 5.5.0f3, 5.5.2p1, 5.6.0b7
Regression introduced in : 5.6.0b8

Workaround : Enable auto generate in lightning settings or disable lightmap static function.