Reproduction steps:
1. Open the attached “repro_IN-72399“ project
2. Open the Entities Hierarchy window (“Window → Entities → Hierarchy“)
3. While having the Entities Hierarchy tab open, open the Package Manager
4. Remove any package (for example, the “Timeline“ package)

Expected result: No errors show up in the Console
Actual result: “NullReferenceException: Object reference not set to an instance of an object“ error shows up in the Console

Reproducible with: 1.0.14 (2023.2.17f1), 1.2.0 (2022.3.23f1, 2023.2.17f1, 6000.0.0b14)
Not reproducible with: 0.51.1-preview.21 (2021.3.37f1), 1.0.11 (2023.2.17f1)

Reproducible on: Windows 10 (22H2)
Not reproducible on: No other environments tested

Note: The error appears both after removing and after installing a package