Null ref exception at GraphControlTest.MainPage in GraphControlSilverlight\GraphControlTest

at GraphControlTest of GraphContorlSilverlight.sln, at MainPage.xaml.cs, the following code

   private void LayoutGeometry_Click(object sender, RoutedEventArgs e)
    {
        var dgraph = FromGeometryContainer.Children[0] as DGraph;
        var dg = dgraph.Graph;
        GeometryTest.Layout(dg.GeometryGraph);
        dgraph.Invalidate();
    }

results in null ref exeption at "var dg = dgraph.Graph" because the "Children[0]" of the container is returning a Button, not a DGraph, so the "as DGraph" gives null

this error occurs at last page of that SL demo, by pressing Layout button at that tab (I see nothing in the graph display btw in that page)

have also tried first pressing the "Geometry Test" button which may be unrelated to that page though since it always appears at top-right, not only when you have that last tab page selected (not sure what that button does either)

Start in GraphControlSilverlight\GraphControlTest, especially MainPage.xaml.cs and LayoutGeometry_Click. Reproduce the failure on the last demo tab by pressing Layout, then inspect how FromGeometryContainer.Children is populated and why its first child is a Button. Done means the Layout action no longer raises the null-reference exception and the intended graph display behavior is verified.