NullReferenceException occurs on deleting Animation Override Controller

Steps to Repro:
1. Create a new Project
2. Create a new Animation Override Controller in the Project Window
2. Delete the Animation Override Controller using the context menu in the Project Window

Actual Result:
NullReferenceException occurs

Expected Result:
Animation Override Controller gets deleted gracefully

Environment:
Windows and Mac

Occurring with:
2019.3.0a4, 2019.3.0a1

Working with:
2019.2.0b4, 2019.1.4f1

Stack Trace:
NullReferenceException: Object reference not set to an instance of an object
UnityEditor.AnimatorOverrideControllerInspector.OnDisable () (at C:/buildslave/unity/build/Editor/Mono/Inspector/AnimatorOverrideControllerInspector.cs:55)