[MAUI] I4_ Selection - Click the 'Single pre-selection for Vertical list ' item will throw an exception: Object reference not set to an instance of an object

[ninachen03]

Description

Affected case: I4:Single Pre-selection (Vertical list)

Steps to Reproduce

1. Deploy https://devdiv.visualstudio.com/Pkgs/_git/VS.TestAssets.Xaml?path=/Assets/Projects/ManualMauiTests to Windows.
2. Navigate to 'I CollectionView' ->'I4 Selection '
3. Open Single Pre-selection (Vertical list) page.

Actual Behavior:

Expected Behavior: Open normally

Link to public reproduction project repository

https://devdiv.visualstudio.com/Pkgs/_git/VS.TestAssets.Xaml?path=/Assets/Projects/ManualMauiTests

Version with bug

Microsoft.Maui.Controls 8.0.70-ci.net8.24328.1

Is this a regression from previous behavior?

Not a regression, the issue also repro on 8.0.61& 8.0.3

Affected platforms

Windows

Relevant log output

System.NullReferenceException
  HResult=0x80004003
  Message=Object reference not set to an instance of an object.
  Source=ManualMauiTests
  StackTrace:
   at ManualMauiTests.ViewModels.MonkeysViewModel.MonkeySelectionChanged() in C:\Users\admin\Desktop\ManualMauiTests\ManualMauiTests\ViewModels\MonkeysViewModel.cs:line 232