code: @Override
      public Void call() throws Exception {
          try {
              final Processor proc = new Processor(false);
              final Configuration config = proc.getUnderlyingConfiguration();
              final NodeInfo doc = new DocumentWrapper(mSession, config);
              final XQueryCompiler comp = proc.newXQueryCompiler();
              final XQueryExecutable exp = comp.compile(mExpression);
  
              if (mSerializer == null) {
                  final Serializer out = new Serializer();
                  out.setOutputProperty(Serializer.Property.METHOD, "xml");
                  out.setOutputProperty(Serializer.Property.OMIT_XML_DECLARATION, "yes");
                  out.setOutputStream(mOut);
                  mSerializer = out;
              }
  
              final net.sf.saxon.s9api.XQueryEvaluator exe = exp.load();
              exe.setSource(doc);
              exe.run(mSerializer);
              return null;
          } catch (final SaxonApiException e) {
              LOGGER.error("Saxon Exception: " + e.getMessage(), e);
              throw e;
          }
      }
docs: {@inheritDoc}