How to reproduce:
1. Open attached project "InspectorLockSignalEmitterIssue_1" and scene "ProblemScene"
2. Select "Sphere" in the Hierarchy and lock its Inspector window by pressing the lock icon in the top right
3. Select "Cube" from the Hierarchy window to see its timeline
4. Click on any track in the CubeTimeline
5. Observe Console window

Expected result: Console window should remain empty
Actual result: Console window outputs multiple NullReferenceException messages

Reproducible with: 2019.1.0a12, 2019.1.0a13
Not reproducible with: 2019.1.0a11
Could not test with: 2019.1.0a10 and older (Timeline Signals not present)

Note: this only happens when the locked object is the receiver of a Signal track in the Timeline