Forcing XDocument.ToString() to include the closing tag when there is no data

Set the Value property of each empty XElement specifically to an empty string.

    // Note: This will mutate the specified document.
    private static void ForceTags(XDocument document)
    {
        foreach (XElement childElement in
            from x in document.DescendantNodes().OfType<XElement>()
            where x.IsEmpty
            select x)
        {
            childElement.Value = string.Empty;
        }
    }