Steps to reproduce (repro video attached):

1. Create a new Unity project
2. Add an empty game object in the Hierarchy
3. Add Mesh Renderer OR Fixed Joint OR Collider OR any other component which has a property of reference type
4. Press the selection circle on the right to the properties reference window

Actual result: Selection window doesn't open and NullReferenceException is thrown instead
Expected behavior: Selection window opens

Reproducible with: 2017.3.0b2

Not reproducible with: 2017.2.0f1, 2017.3.0a7

Regression introduced in 2017.3.0b1