Category disappears from the blackboard window when renamed with an empty string

Steps to repro:
1. Open the attached project.
2. Packages > Visual Effect Graph > Editor > Templates > Open Empty Particle System.
3. Select Blackboard tab > Add Category.
4. Right-click on new category > Rename with an empty string.

Actual Result:
Category disappears from the blackboard window.

Expected Result:
The category appears in the blackboard window

Reproducible in:
2019.3.0a12, 2019.3.0a10.

NOTE:
1. Visual Effects introduced in 2019.3.0a10.
2. Could not test on Mac due to https://fogbugz.unity3d.com/f/cases/1174796/

Environment:
Only on Windows.