On creating prefab of the GameObject which has the "SpriteSkin" component added causes the editor to throw NullReferenceException continuously, refer the attached video.

Steps to repro:
1. Create a new project
2. Windows > Package Manager > 2D Animation > Install
3. Hierarchy > right-click > Create Empty
4. Inspector > Add Component > 2D Animation > Sprite Skin > Add
5. Create Prefab of that Object.

Actual Result:
NullReferenceException is thrown when prefab of the Object is created which has "Sprite Skin" component is added

Expected Result:
Prefab of the object created gracefully which has "Sprite Skin" component added

Reproducible in:
2020.2.0a11, 2020.1.0b9, 2020.1.0a13 with Package Version: 4.2.2.

Working fine in:
2020.2.0a11, 2020.1.0b9, 2020.1.0a13 with Package Version: 4.2.1.

Environment:
Windows 10 & macOS 10.14

Stacktrace:
NullReferenceException: Object reference not set to an instance of an object
UnityEditor.U2D.Animation.SpriteSkinEditor.OnEnable () (at Library/PackageCache/com.unity.2d.animation@4.2.2/Editor/SpriteSkin/SpriteSkinEditor.cs:60)