How to reproduce:
1. Create a new Unity project
2. Go to Edit -> Project Settings -> Graphics -> Shader Build Settings
3. Add an item under the "Keyword Declaration Overrides"
4. Enter any character, double-space, and another character 
5. Expand the keywords list and observe the results

Expected results: Only two keywords are on the list
Actual results: There are three keywords on the list, one of which is empty

Reproducible with: 6000.3.1f1, 6000.4.0b1, 6000.5.0a3
Can't test with: 6000.0.64f1, 6000.2.15f1, 6000.3.0f1, 6000.4.0a5 (No expandable list)

Reproducible on: Windows 11 Pro
Not reproducible on: No other environment tested

Note: Empty keywords are not removed when deleting everything from the field, list item should be readded