HtmlFromXamlConverter.cs crashes when there is a FontSize attribute on the FlowDocument itself and asFullDocument=false

It throws me a System.IndexOutOfRangeException at line 493.

   bij System.Xml.XmlTextWriter.WriteEndStartTag(Boolean empty)
   bij System.Xml.XmlTextWriter.AutoComplete(Token token)
   bij System.Xml.XmlTextWriter.WriteStartElement(String prefix, String localName, String ns)
   bij System.Xml.XmlWriter.WriteStartElement(String localName)
   bij MarkupConverter.HtmlFromXamlConverter.WriteElement(XmlTextReader xamlReader, XmlTextWriter htmlWriter, StringBuilder inlineStyle) in C:\Users\Laïla\Downloads\Converting between RTF and HTML\C#\MarkupConverter\HtmlFromXamlConverter.cs:regel 530
   bij MarkupConverter.HtmlFromXamlConverter.WriteElementContent(XmlTextReader xamlReader, XmlTextWriter htmlWriter, StringBuilder inlineStyle) in C:\Users\Laïla\Downloads\Converting between RTF and HTML\C#\MarkupConverter\HtmlFromXamlConverter.cs:regel 379
   bij MarkupConverter.HtmlFromXamlConverter.WriteFlowDocument(XmlTextReader xamlReader, XmlTextWriter htmlWriter, Boolean asFullDocument) in C:\Users\Laïla\Downloads\Converting between RTF and HTML\C#\MarkupConverter\HtmlFromXamlConverter.cs:regel 120
   bij MarkupConverter.HtmlFromXamlConverter.ConvertXamlToHtml(String xamlString, Boolean asFullDocument) in C:\Users\Laïla\Downloads\Converting between RTF and HTML\C#\MarkupConverter\HtmlFromXamlConverter.cs:regel 67
   bij FormatBarForRichTextBox.MainWindow.Button_Click_6(Object sender, RoutedEventArgs e) in C:\Users\Laïla\Downloads\FormatBarForRichTextBox\FormatBarForRichTextBox\FormatBarForRichTextBox\MainWindow.xaml.cs:regel 277