"Sprite Library Assets" is created in the project view which has the option of Adding New Category. While adding new category there are below issues
1. A new Category is not being added.
2. IndexOutOfRangeException is thrown continuously when a created "Sprite Library Assets" is selected.
3. When "Sprite Library Assets" is not selected, exception stops occurring until the asset is selected again.
4. Re-importing or Restarting project and selecting "Sprite Library Assets" causes the exception to appear again
5. The exception can not be cleared as it is continuous.
6. Deleting the "Sprite Library Assets" or not selecting it in the project window stops the exception to appear.
7. There is no workaround using which a category is added to the "Sprite Library Assets"
, refer to the attached video.

Steps to repro:
1. Create Project with 2D Template
2. Project > Create > Sprite Library Assets
3. Inspector > Add New Category

Actual Result:
IndexOutOfRangeException is thrown continuously on adding New Category in Sprite Library Asset

Expected Result:
New Category added without throwing any exception in the console

Note:
There is no workaround using which a category can be added in the "Sprite Library Assets".

Reproducible on:
2020.2.0a13 with Package version 4.2.4.

Working fine on:
2020.2.0a12, 2020.1.0b11 with Package version 4.2.4.

Environment:
Windows 10 & macOS 10.14