System.NullReferenceException (Radio buttons)
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I have two radio buttons and if i put the attribute ischecked in xaml the program crash with System.NullReferenceException and Additional information: Object reference not set to an instance of an object.
My radio buttons: 
`<RadioButton IsChecked="True" Name="Mint" Checked="Mint_Checked_1" Foreground="Red"  FlowDirection="RightToLeft"  VerticalAlignment="Top" HorizontalAlignment="Right"  Margin="10,30,10,0" GroupName="Update_When" Content="A"></RadioButton>
  <RadioButton IsChecked="False" Name="Changet" Checked="Changet_Checked_1" FlowDirection="RightToLeft" VerticalAlignment="Top" HorizontalAlignment="Right"  Margin="10,53,10,0" GroupName="Update_When" Content="B"></RadioButton>`

       