How to reproduce:
1. Open the attached '1301021.zip' project
2. Select Help > Quick Search
3. In the search bar enter 'Test'
4. In the Quick Search window select the Test Asset
5. Observe the Console

Expected result: No visible errors present
Actual result: MissingReferenceException errors appear in the Console

Reproducible with: Quick Search 1.6.0-preview.5 (2019.4.17f1, 2020.1.17f1), 3.0.0-preview.1 (2020.1.17f1, 2020.2.0f1)
Not reproducible with: Quick Search 1.6.0-preview.4 (2019.4.17f1, 2020.1.17f1), 3.0.0-preview.2 (2020.1.17f1, 2020.2.0f1), 3.0.0-preview.3 (2020.2.0f1), 2021.1.0b1 (the Quick Search is part of the Unity Editor)
Cannot test with: Quick Search 1.6.0-preview.4 (2018.4.30f1, 2020.2.0f1), 3.0.0-preview.3 (2018.4.30f1, 2019.4.17f1, 2020.1.17f1) (the Quick Search package versions are not supported)

Notes:
- The issue does not reproduce with .uss files
- After selecting the .tss file NullReference exceptions get thrown in the Console