How to reproduce:
1. Create a new project
2. Import the HD RP package from the Package Manager
3. In the Hierarchy window create a new GameObject
4. Add the 'Decal Projector' Component to the newly created GameObject
5. Make sure that the 'Material' field in the 'Decal Projector' Component is not assigned
6. Duplicate the GameObject at least 1 time
7. Select at least two GameObjets that have the 'Decal Projector' Component

Expected result: the GameObjects are selected successfully
Actual result: GameObject are selected but an error occurs: 'NullReferenceException: Object reference not set to an instance of an object'

Reproducible with: 5.3.1-preview (2019.3.0a1), 7.3.1 (2019.4.12f1), 8.2.0 (2020.1.9f1), 9.0.0-preview.54 (2020.2.0b6), 10.0.0-preview.27 (2020.2.0b7, 2021.1.0a2), 10.1.0 (2021.1.0a2)
Not reproducible with: 4.10.0-preview (2018.4.29f1), 5.2.3-preview (2019.3.0a1)