Showing a document that contains a Table object without any TableRow inside leads to NullReferenceException.

Workaround: After importing the document, remove the tables that don't have content:

foreach (var table in document.EnumerateChildrenOfType<Table>())
{
    if (table.Rows.Count < 1)
    {
        table.Parent.Children.Remove(table);
    }
}

To reproduce:

1. Insert content spanning 3 pages
2. Ensure a single page is visualized in the viewport 
3. Start selecting from the beginning of the content till the end by dragging the mouse
4. Press Delete

The issue is a regression introduced in R3 2021 SP1.

The parent of an already removed span cannot be found and a NullReferenceException is thrown while performing Undo. Also, multiple asserts are failing in Debug mode. The stack trace is:

UnhandledException: Object reference not set to an instance of an object.
UnhandledException:   at Telerik.Windows.Documents.Layout.LayoutElement.SetParent(LayoutElement newParent)
   at Telerik.Windows.Documents.Layout.LayoutBox.EnsureParent()
   at Telerik.Windows.Documents.Layout.LayoutBox.get_Parent()
   at Telerik.Windows.Documents.Layout.LayoutBox.get_ValidParent()
   at Telerik.Windows.Documents.WordPositionHandler.GetParentHandler()
   at Telerik.Windows.Documents.DocumentPosition.GetCurrentSectionBox()
   at Telerik.Windows.Documents.UI.DocumentPrintLayoutPresenter.GetCurrentPage()
   at Telerik.Windows.Documents.UI.DocumentPrintLayoutPresenter.MeasureOverride(Size availableSize)
   at System.Windows.FrameworkElement.MeasureCore(Size availableSize)