document-uri gone when using Saxon.API .NET?

    public static string Transform(string xml, string xsl, Uri xmlBaseUri, Uri xslBaseUri, NameValueCollection transParams)
    {
        // Load the source document
        DocumentBuilder builder = processor.NewDocumentBuilder();
        builder.BaseUri = xmlBaseUri;
        Stream xmlStream = new MemoryStream(Encoding.UTF8.GetBytes(xml));
        XdmNode input = builder.Build(xmlStream);
        xmlStream.Close();

        // Compile the stylesheet
        XsltCompiler compiler = processor.NewXsltCompiler();
        compiler.BaseUri = xslBaseUri;
        Stream xslStream = new MemoryStream(Encoding.UTF8.GetBytes(xsl));
        XsltExecutable exec = compiler.Compile(xslStream);
        xslStream.Close();

        // Create transformer with parameters
        XsltTransformer transformer = exec.Load();
        foreach(string key in transParams.AllKeys) {
            transformer.SetParameter(new QName("", "", key), new XdmAtomicValue(transParams[key]));
        }

        // Run
        transformer.InitialContextNode = input;
        XdmDestination results = new XdmDestination();
        transformer.Run(results);

        return results.XdmNode.StringValue;
    }

    public static string Transform(Uri xml, Uri xsl, NameValueCollection transParams)
    {
        // Load the source document
        DocumentBuilder builder = processor.NewDocumentBuilder();
        XdmNode input = builder.Build(xml);

        // Compile the stylesheet
        XsltCompiler compiler = processor.NewXsltCompiler();
        XsltExecutable exec = compiler.Compile(xsl);

        // Create transformer with parameters
        XsltTransformer transformer = exec.Load();
        foreach(string key in transParams.AllKeys) {
            transformer.SetParameter(new QName("", "", key), new XdmAtomicValue(transParams[key]));
        }

        // Run
        transformer.InitialContextNode = input;
        XdmDestination results = new XdmDestination();
        transformer.Run(results);

        return results.XdmNode.StringValue;
    }