Repro steps:
1. Open user attached project
2. Open scene "SampleScene"
3. Select "ThirdPersonController" in the Hierarchy
4. Notice the warning in the Console: "Creating editor inspector failed: input objects don't reference to the same script."
5. See the "Nothing Selected (Removed)" components in the Inspector, right click on them and observe the Console
6. Notice the message in the Inspector: "Components that are only on some of the selected objects cannot be multi-edited"
7. Open the prefab in Prefab Mode and notice that missing components are gone

Expected: You're able to see and remove missing or removed components in Prefab Mode.
Actual: NullReferenceException is thrown when right-clicking missing components in the Inspector. Missing components dis-appear in Prefab Mode and can't be removed. A warning appears in the Console when selecting the Prefab.

Reproducible with: 2018.3.0b3, 2019.1.0a2

Fixed in: 2019.1.0a6