ArgumentOutOfRangeException is thrown continuously when Rule Tile is Reset and adding Tiling Rules in the List from Inspector, Refer to attached video.

Steps to repro:
1. Create a new project with a 2D Template
2. Window > Package Manager > 2D Tilemap Extras > Install
3. Project > Create > 2D > Tiles > Rule, Hexagonal, Isometric Tile
4. Inspector > Tiling Rules > Add
5. Burger button > Reset
6. Try to add again Tiling Rules

Actual Result:
ArgumentOutOfRangeException is thrown on adding Tiling Rules under Rule Tile in Inspector after resetting the existed list

Expected Result:
Tiling Rules are added gracefully in the List

Note: Rule, Isometric, Hexagonal Tiles are introduced in the Unity 2021.2.0a6

Reproducible in:
2021.2.0a16, 2021.2.0a6

Environment:
Occurring on Windows 10 & macOS 10.15.

Stack trace:
ArgumentOutOfRangeException: Index must be within the bounds of the List.
Parameter name: index
System.ThrowHelper.ThrowArgumentOutOfRangeException (System.ExceptionArgument argument, System.ExceptionResource resource) (at <695d1cc93cca45069c528c15c9fdd749>:0)
System.Collections.Generic.List`1[T].Insert (System.Int32 index, T item) (at <695d1cc93cca45069c528c15c9fdd749>:0)
UnityEditor.RuleTileEditor.OnAddElement (System.Object obj) (at Library/PackageCache/com.unity.2d.tilemap.extras@2.0.0/Editor/Tiles/RuleTile/RuleTileEditor.cs:276)
UnityEditor.RuleTileEditor.OnAddDropdownElement (UnityEngine.Rect rect, UnityEditorInternal.ReorderableList list) (at Library/PackageCache/com.unity.2d.tilemap.extras@2.0.0/Editor/Tiles/RuleTile/RuleTileEditor.cs:304)
UnityEditorInternal.ReorderableList+Defaults.DrawFooter (UnityEngine.Rect rect, UnityEditorInternal.ReorderableList list) (at <03609da0ab2f44f1b4469aa7e2ed6dad>:0)
UnityEditorInternal.ReorderableList.DoListFooter (UnityEngine.Rect footerRect) (at <03609da0ab2f44f1b4469aa7e2ed6dad>:0)
UnityEditorInternal.ReorderableList.DoLayoutList () (at <03609da0ab2f44f1b4469aa7e2ed6dad>:0)
UnityEditor.RuleTileEditor.OnInspectorGUI () (at Library/PackageCache/com.unity.2d.tilemap.extras@2.0.0/Editor/Tiles/RuleTile/RuleTileEditor.cs:404)
UnityEditor.UIElements.InspectorElement+<>c__DisplayClass59_0.<CreateIMGUIInspectorFromEditor>b__0 () (at <e6e1a2d577f64f5ca07dab289b4fed14>:0)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr, Boolean&)