"MissingReferenceException" error thrown after clicking browse button of Preset slot in Preset Manager.

Steps to Reproduce:
1. Open an attached project or create a new project.
2. Create any Unity primitive. (Ex. Cube)
3. Click on the preset icon at the right of the BoxCollider component bar.
4. From the "Select Preset" window, click on the "Save current to" button to Save the preset.
5. Create another preset of same BoxCollider component with the different name. (Ex. BoxCollider123)
6. Go to Settings -> Preset Manager
7. Dock Preset Manager window anywhere in the editor.
8. Click on '+' icon -> UnityEngine -> BoxCollider -> BoxCollider123
9. Delete 'BoxCollider123' preset from Project window.
10. The corresponding preset slot in the PresetManager should display the text: "Missing (Preset)", click on browse button of that preset slot.

Note: If user wants to reproduce from the attached project, he needs to start from Step: 5

Actual Result:
MissingReferenceException thrown upon clicking browse button of Preset slot.

Expected Result:
By clicking on the browse button, a simple list should appear showing the available preset for that type. In the above Scenario, it should show 'BoxCollider' preset in the available preset list.

Environment:
Windows and Mac

Occurring with :
2018.3.0a8, 2018.3.0a3, 2018.3.0a1

Working fine with :
2018.2.0f2

Error Details :
MissingReferenceException: The object of type 'Preset' 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.
UnityEngine.Object.get_name () (at C:/buildslave/unity/build/Runtime/Export/UnityEngineObject.bindings.cs:198)
UnityEditor.Presets.PresetManagerEditor.DrawElementCallback (UnityEngine.Rect rect, System.Int32 index, System.Boolean isActive, System.Boolean isFocused) (at C:/buildslave/unity/build/Modules/PresetsEditor/PresetManagerEditor.cs:156)
UnityEditorInternal.ReorderableList.DoListElements (UnityEngine.Rect listRect) (at C:/buildslave/unity/build/Editor/Mono/GUI/ReorderableList.cs:587)
Unit