After creating a Probuilder Gameobject, on selecting UV Editor Window NullReferenceException and ArgumentException threw in console, refer attached video and stack trace.

Steps to repro:
1. Create a new project.
2. Window > Package Manager> ProBuilder[Install].
3. Tools > ProBuilder > ProBuilder Window
4. ProBuilder Window > New Shape > Create Cube and select
5. Open UV Editor from ProBuilder window

Actual Result:
ArgumentNullException and NullReferenceException errors are thrown in the console.

Expected Result:
No error in the console.

Reproducible in:
2020.2.0a9 with Package Version 4.2.3, 4.3.0-preview.7

Working fine in:
2020.2.0a8, 2020.1.0b8 with Package Version 4.2.3, 4.3.0-preview.7
2019.3.6f1 with Package Version 4.2.3

Environment:
Windows 10 & macOS 10.15