[AR][iOS] Null reference errors start on switching to iOS platform with ARFoundation samples project

Once the platform is changed to iOS null reference and Invalid caste errors appear in the console. These errors then occur every time the player settings window is open-door any asset is selected from the project window

Steps To Reproduce:

1. Download ARFoundation Samples project: https://github.com/Unity-Technologies/arfoundation-samples
2. HUB > Add> "ARFoundation Samples" and
3. Select iOS platform
4. Open the project and observe

Expected Result: Project opens up without any issues/errors

Observed result: Null reference error appears in the console

Note:
1. The error occurs every time opening the player settings window
2. The error also occurs on clicking on assets in project window

Reproducible In: 2021.1.0a3, 2020.2.0b9

Reproducible with package version: 4.1.0

Not reproducible with package version: 4.0.9

Environment: Occurs only on mac

Stack trace:
1. NullReferenceException: Object reference not set to an instance of an object
UnityEditor.PlayerSettingsEditor.UpdateScriptingDefineSymbolsLists () (at /Users/bokken/buildslave/unity/build/Editor/Mono/Inspector/PlayerSettingsEditor/PlayerSettingsEditor.cs:3147)
UnityEditor.PlayerSettingsEditor.CheckConsistency (UnityEditor.BuildTargetGroup targetGroup) (at /Users/bokken/buildslave/unity/build/Editor/Mono/Inspector/PlayerSettingsEditor/PlayerSettingsEditor.cs:701)
UnityEditor.PlayerSettingsEditor.OnInspectorGUI () (at /Users/bokken/buildslave/unity/build/Editor/Mono/Inspector/PlayerSettingsEditor/PlayerSettingsEditor.cs:835)
UnityEditor.AssetSettingsProvider.OnGUI (System.String searchContext) (at /Users/bokken/buildslave/unity/build/Editor/Mono/Settings/Providers/AssetSettingsProvider.cs:92)
UnityEditor.SettingsWindow.DrawControls () (at /Users/bokken/buildslave/unity/build/Editor/Mono/Settings/SettingsWindow.cs:407)
UnityEditor.SettingsWindow.DrawSettingsPanel () (at /Users/bokken/buildslave/unity/build/Editor/Mono/Settings/SettingsWindow.cs:385)
UnityEngine.UIElements.IMGUIContainer.DoOnGUI (UnityEngine.Event evt, UnityEngine.Matrix4x4 parentTransform, UnityEngine.Rect clippingRect, System.Boolean isComputingLayout, UnityEngine.Rect layoutSize, System.Action onGUIHandler, System.Boolean canAffectFocus) (at /Users/bokken/buildslave/unity/build/External/MirroredPackageSources/com.unity.ui/Core/IMGUIContainer.cs:333)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr, Boolean&) (at /Users/bokken/buildslave/unity/build/Modules/IMGUI/GUIUtility.cs:189)

2. InvalidCastException: Specified cast is not valid.
UnityEditor.EditorGUILayout.BeginScrollView (UnityEngine.Vector2 scrollPosition, System.Boolean alwaysShowHorizontal, System.Boolean alwaysShowVertical, UnityEngine.GUIStyle horizontalScrollbar, UnityEngine.GUIStyle verticalScrollbar, UnityEngine.GUIStyle background, UnityEngine.GUILayoutOption[] options) (at /Users/bokken/buildslave/unity/build/Editor/Mono/EditorGUI.cs:9891)
UnityEditor.EditorGUILayout.BeginScrollView (UnityEngine.Vector2 scrollPosition, UnityEngine.GUILayoutOption[] options) (at /Users/bokken/buildslave/unity/build/Editor/Mono/EditorGUI.cs:9861)
UnityEditor.EditorGUILayout+ScrollViewScope..ctor (UnityEngine.Vector2 scrollPosition, UnityEngine.GUILayoutOption[] options) (at /Users/bokken/buildslave/unity/build/Editor/Mono/EditorGUI.cs:9820)
UnityEditor.SettingsWindow.DrawSettingsPanel () (at /Users/bokken/buildslave/unity/build/Editor/Mono/Settings/SettingsWindow.cs:382)
UnityEngine.UIElements.IMGUIContainer.DoOnGUI (UnityEngine.Event evt, UnityEngine.Matrix4x4 parentTransform, UnityEngine.Rect clippingRect, System.Boolean isComputingLayout, UnityEngine.Rect layoutSize, System.Action onGUIHandler, System.Boolean canAffectFocus) (at /Users/bokken/buildslave/unity/build/External/MirroredPackageSources/com.unity.ui/Core/IMGUIContainer.cs:353)
UnityEngine.UIElements.IMGUIContainer.HandleIMGUIEvent (UnityEngine.Event e, UnityEngine.Matrix4x4 worldTransform, UnityEngine.Rect clippingRect, System.Action onGUIHandler, System.Boolean canAffectFocus) (at /Users/bokken/buildslave/unity/build/External/MirroredPackageSources/com.unity.ui/Core/IMGUIContainer.cs:663)
UnityEngine.UIElements.IMGUIContainer.DoIMGUIRepaint () (at /Users/bokken/buildslave/unity/build/External/MirroredPackageSources/com.unity.ui/Core/IMGUIContainer.cs:530)
UnityEngine.UIElements.UIR.RenderChainCommand.ExecuteNonDrawMesh (UnityEngine.UIElements.UIR.DrawParams drawParams, System.Single pixelsPerPoint, System.Exception& immediateException) (at /Users/bokken/buildslave/unity/build/External/MirroredPackageSources/com.unity.ui/Core/Renderer/UIRenderer/UIRenderers.cs:114)
Rethrow as ImmediateModeException
UnityEngine.UIElements.UIR.RenderChain.Render () (at /Users/bokken/buildslave/unity/build/External/MirroredPackageSources/com.unity.ui/Core/Renderer/UIRChainBuilder.cs:510)
UnityEngine.UIElements.UIRRepaintUpdater.Update () (at /Users/bokken/buildslave/unity/build/External/MirroredPackageSources/com.unity.ui/Core/Renderer/UIRRepaintUpdater.cs:62)
UnityEngine.UIElements.VisualTreeUpdater.UpdateVisualTreePhase (UnityEngine.UIElements.VisualTreeUpdatePhase phase) (at /Users/bokken/buildslave/unity/build/External/MirroredPackageSources/com.unity.ui/Core/VisualTreeUpdater.cs:83)
UnityEngine.UIElements.Panel.UpdateForRepaint () (at /Users/bokken/buildslave/unity/build/External/MirroredPackageSources/com.unity.ui/Core/Panel.cs:833)
UnityEngine.UIElements.Panel.Repaint (UnityEngine.Event e) (at /Users/bokken/buildslave/unity/build/External/MirroredPackageSources/com.unity.ui/Core/Panel.cs:869)
UnityEngine.UIElements.UIElementsUtility.DoDispatch (UnityEngine.UIElements.BaseVisualElementPanel panel) (at /Users/bokken/buildslave/unity/build/External/MirroredPackageSources/com.unity.ui/Core/UIElementsUtility.cs:441)
UnityEngine.UIElements.UIElementsUtility.UnityEngine.UIElements.IUIElementsUtility.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr, System.Boolean& eventHandled) (at /Users/bokken/buildslave/unity/build/External/MirroredPackageSources/com.unity.ui/Core/UIElementsUtility.cs:209)
UnityEngine.UIElements.UIEventRegistration.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr) (at /Users/bokken/buildslave/unity/build/External/MirroredPackageSources/com.unity.ui/Core/UIElementsUtility.cs:74)
UnityEngine.UIElements.UIEventRegistration+<>c.<.cctor>b__1_2 (System.Int32 i, System.IntPtr ptr) (at /Users/bokken/buildslave/unity/build/External/MirroredPackageSources/com.unity.ui/Core/UIElementsUtility.cs:28)
UnityEngine.GUIUtility.ProcessEvent (System.Int32 instanceID, System.IntPtr nativeEventPtr, System.Boolean& result) (at /Users/bokken/buildslave/unity/build/Modules/IMGUI/GUIUtility.cs:189)