When "New Animator Controller" is deleted and hide the "Layers" and "Parameters" panel in the "Animator" window after that selecting the "Layers" dropdown causes the editor to throw MissingReferenceException, refer attached video.

Steps to repro:
1. Create a new project
2. Project window > Create > Animator Controller
3. Project > New Animator Controller > Double-click
4. Animator > Layer Blackboard > right-click > Create State > From New Blend Tree
5. Blend Tree > double-click
6. Project >New Animator Controller > Delete
7. Select the eye icon in the Animator window
8. Click on Layer dropdown

Actual Result:
MissingReferenceException is thrown on selecting "Layers" dropdown in the Animator window

Expected Result:
"Layers" dropdown is selected gracefully

Occurring on:
2020.2.0a15, 2020.1.0b12, 2019.3.15f1, 2019.2.13f1, 2019.1.11f1, 2018.4.24f1, 2017.4.40f1

Environment:
Windows10 and macOS 10.14