SwitchPresenter NullReferenceException

[michael-hawker]

Describe the bug

Possible to get a NRE using SwitchPresenter.

Steps to Reproduce

    <StackPanel>
        <TextBox x:Name="MyTextBox" />
        <controls:SwitchPresenter Value="{x:Bind MyTextBox.Text, Mode=OneWay}">
            <controls:Case Value="Magic">
                <TextBlock>Everything you do...</TextBlock>
            </controls:Case>
        </controls:SwitchPresenter>
    </StackPanel>

Enter the text 'Magic' in the text box and the case shows as expected; however removing any text after then causes a NRE.

System.NullReferenceException
  HResult=0x80004003
  Message=Object reference not set to an instance of an object.
  Source=Windows
  StackTrace:
   at Windows.UI.Xaml.DependencyObject.SetValue(DependencyProperty dp, Object value)
   at Microsoft.Toolkit.Uwp.UI.Controls.SwitchPresenter.set_Value(Object value)
   at ControlPackagesTest.MainPage.XamlBindingSetters.Set_Microsoft_Toolkit_Uwp_UI_Controls_SwitchPresenter_Value(SwitchPresenter obj, Object value, String targetNullValue) in ControlPackagesTest\ControlPackagesTest\obj\x86\Debug\MainPage.g.cs:line 28

Expected behavior

No NRE

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[michael-hawker]

I need to create a sample still and I'll see if I can figure it out in the Sample app. May also need to look at using DependencyObjectCollection here as well, so maybe can do final restructuring and test this scenario as well...