Reproduction steps:
1. Open the attached Unity project "Sequences.zip"
2. Open Sequences window (Window > Sequencing > Sequences)
3. Delete the "New Sequence" (New Master Sequence > New Sequence > Right-click > Delete)
4. Observe the Console window

Expected result: No errors in the Console window
Actual result: An error message is thrown in the Console window

Reproducible with: 1.0.0-pre.4, 1.0.0-pre.5, 1.0.0-pre.6, 1.0.0 (2020.3.16f1, 2021.2.0b7, 2022.1.0a5)
Can't test with: 2019.4.29f1 (no Sequences window, Console errors)

Notes:
- Steps might need to be repeated several times for error to be thrown
- When creating new Sequences in New Master Sequence, it often creates an empty (red) New Sequence