Does NullValue have an internally set value?

[Gleedo]

We are using 2011 Q1.

I have a RadNumericUpDown setup as the following:

<telerik:RadNumericUpDown Margin="2" Name="GotoPageValue" IsInteger="True" Value="1" ValueChanged="GotoPageValue_ValueChanged" IsEnabled="False" IsEditable="True"></telerik:RadNumericUpDown>

NullValue is not set and when inspected under a debugger in the watch window, it looks like this:
NullValue=""

My problem is this.  When a user has navigated to a value like 2 using the up/down arrows, if they then highlight the value, delete it, and then hit the up arrow, the value always returns to 1.

The NullValue was previously set to 1 which I thought must be causing the problem, but after removing NullValue, the problem continued.

Basically inside the ValueChanged event and want to check if e.NewValue == null and if it is null, change e.NewValue to the previous value + 1.  Is this the wrong thing to do?

private void GotoPageValue_ValueChanged(object sender, RadRangeBaseValueChangedEventArgs e)
      {
         // has user cleared value manually?
         if (e.NewValue == null)
         {
            if (_pageNumber <= GotoPageValue.Maximum)
            {
               // reset back to previous value
               e.NewValue = _pageNumber;
            }
         }

         FireCommandActivated(SearchResultsNavigationToolbarCommand.GotoPageValue, e);

         // remember new value incase user clears value manually and hits up/down
         _pageNumber = (int)e.NewValue;
      }

[Gleedo]

Not to worry - I got around by using PreviewKeyDown and just checking if backspace or delete were being pressed.