On deleting Levels(Very High, High etc..) of Quality Settings from its preset causes editor to throw NullReferenceException continuously also not able to delete other Levels, refer attached video.

Steps to repro:
1. Create a new project.
2. Edit > Project Settings > Quality
3. Create preset of Quality settings
4. Project > QualitySettings > Inspector
5. Delete Levels (Very High, High, Medium, etc..)

Actual Result:
NullReferenceException thrown continuously on deleting the Levels

Expected Result:
Levels are deleted gracefully without any exception thrown

Note: Preset functionality introduced in 2018.1

Tested with Unity Version:
2020.1.0a23, 2019.3.1f1, 2019.2.13f1, 2019.1.11f1, 2018.4.13f1, 2018.1.0f2, 2018.1.0a1

Environment:
Windows 10 & macOS 10.14.

Stack trace:
Retrieving array element that was out of bounds
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr, Boolean&)

NullReferenceException: Object reference not set to an instance of an object
UnityEditor.QualitySettingsEditor.OnInspectorGUI () (at <14e2d4b2ee9f48738146210decad60c4>:0)
UnityEditor.Presets.PresetEditor.DrawInternalInspector () (at <14e2d4b2ee9f48738146210decad60c4>:0)
UnityEditor.Presets.PresetEditor.DrawPresetData () (at <14e2d4b2ee9f48738146210decad60c4>:0)
UnityEditor.Presets.PresetEditor.OnInspectorGUI () (at <14e2d4b2ee9f48738146210decad60c4>:0)
UnityEditor.UIElements.InspectorElement+<>c__DisplayClass58_0.<CreateIMGUIInspectorFromEditor>b__0 () (at <14e2d4b2ee9f48738146210decad60c4>:0)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr, Boolean&)