Exiting Prefab Mode pop up appears along with NullReferenceException on deleting Light Probe prefab from the project view.

Steps to Reproduce:
1. Create a new project.
2. Hierarchy > Create > Light > Light Probe Group
3. Drag and drop Light Probe Group in the project view
4. Open Light Probe Group in Prefab Mode.
5. Delete Light Probe Group prefab from Project view.
6. Select Delete from Delete selected asset popup.

Actual Result:
Exiting Prefab Mode pop up appears along with NullReferenceException and Editor breaks down

Expected Result:
Light Probe prefab gets deleted gracefully.

Note:
Refer attached video.

Reproducible on:
2019.3.0a3, 2019.2.0b3, 2019.2.0a12

Not Reproducible on:
2019.2.0a11

Environment:
Windows and MacOS

Notes:
- The issue happens only when the auto-baking is enabled in the Lighting window and doesn't happen when manual bake is on.