The empty lines are not converted properly from RTF to HTML

Workaround: 

private static void FixEmptyParagraphs(RadFlowDocument document)
{
    var paragraphs = document.EnumerateChildrenOfType<Paragraph>();



    foreach (var paragraph in paragraphs)
    {
        if (paragraph.Inlines.Count < 1)
        {
            char nbsp = (char)160;
            paragraph.Inlines.AddRun(nbsp.ToString());
        }
    }
}