Steps:
1. Create a new scene
2. Drag Directional Light to Project Browser to make a prefab
3. Open this prefab
4. Go back to main scene
==>
"MissingReferenceException: The object of type 'Light' has been destroyed but you are still trying to access it.
Your script should either check if it is null or you should not destroy the object."

5. Click on Directional Light prefab instance in the Hierarchy
==>
"The serializedObject should not be used inside OnSceneGUI or OnPreviewGUI. Use the target property directly instead."

Note: Also repro if Ausio Source is added in Prefab mode to prefab asset.

Take a look into attached movie for details

Not repro in Version 2019.1.0a13 (3de2277bb0e6)