SerializedObject target has been destroyed error is thrown on creating Lightmap Parameter in LightingSettings Preset.

Steps to repro:
1. Create a new Project.
2. Project > Assets > Scenes > SampleSceneSettings.
3. Create SampleSceneSettings preset.
4. Create new Lightmap Parameter in the preset asset.

Actual Result:
SerializedObject target has been destroyed error in the console.

Expected Result:
No Errors in the console.

Reproducible in:
2020.1.0a18, 2020.1.0a16.

Environment:
Windows & Mac.

NOTE: Creating the Lightmap Parameter in Preset asset introduced in 2020.1.0a16.

Stack trace:
SerializedObject target has been destroyed.
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)