Saxon

I am having trouble to find a way to use a Serializer on .NET to output the result of an XQuery that is not XML, like a map, when the XQuery uses declare option output:method "adaptive"; that should allow for a flexible and dynamic output method.

A reduced test case run against Saxon 9.8.0.6 HE is

            Processor processor = new Processor(false);
            XQueryCompiler compiler = processor.NewXQueryCompiler();

            XQueryEvaluator evaluator = compiler.Compile("declare namespace output = \"http://www.w3.org/2010/xslt-xquery-serialization\"; declare option output:method \"adaptive\"; map { 'string' : 'foo', 'number' : 1, 'boolean' : true() }").Load();

            Serializer serializer = processor.NewSerializer(Console.Out);

            evaluator.Run(serializer);

and throws the following stack trace:

java.lang.UnsupportedOperationException occurred
  HResult=0x80131500
  Message=A map has no string value
  Source=<Cannot evaluate the exception source>
  StackTrace:
   at net.sf.saxon.ma.map.HashTrieMap.getStringValueCS()
   at net.sf.saxon.serialize.UncommittedSerializer.append(Item item, Location locationId, Int32 copyNamespaces)
   at net.sf.saxon.expr.Literal.process(XPathContext context)
   at net.sf.saxon.query.XQueryExpression.run(DynamicQueryContext env, Result result, Properties outputProperties)
   at Saxon.Api.XQueryEvaluator.Run(XmlDestination destination)
   at Saxon98XQueryTest.Program.Main(String[] args) in c:\users\martin honnen\documents\visual studio 2017\Projects\Saxon98XQueryTest\Saxon98XQueryTest\Program.cs:line 21

A similar Java program

        Processor processor = new Processor(false);
        XQueryCompiler compiler = processor.newXQueryCompiler();
        
        XQueryEvaluator evaluator = compiler.compile("declare namespace output = \"http://www.w3.org/2010/xslt-xquery-serialization\"; declare option output:method \"adaptive\"; map { 'string' : 'foo', 'number' : 1, 'boolean' : true() }").load();
        
        Serializer serializer = processor.newSerializer(System.out);
        
        evaluator.run(serializer);

however runs fine and outputs the map as

map{"boolean":true(),"number":1,"string":"foo"}

What code do I need on the .NET side to write XQuery results to a Serializer so that the output options in the code are honoured, like it works on the Java side?