error while converting to html: System.ArgumentNullException: Value cannot be null. Parameter name: rtfDocument at Itenso.Rtf.Converter.Html.RtfHtmlConverter..ctor(IRtfDocument rtfDocument, RtfHtmlConvertSettings settings) at RTFHTML.ConvertHtml(IRtfDocument rtfDocument, IRtfVisualImageAdapter imageAdapter, String sSourceFileNameWithoutExtension, String sImagesPath, Boolean bShowHiddenText, RtfHtmlConvertScope conversionScope, String sStyleSheetsLinks, Boolean bConvertVisualHyperLinks)