code: public String toXML() {
          Error error = getError();
  
          if (error != null) {
              return error.toXML();
          }
  
          StringWriter sw = new StringWriter();
          String xml = "";
  
          try {
              JAXBContext context = JAXBContext.newInstance(this.getClass());
              Marshaller marshaller = context.createMarshaller();
  
              marshaller.marshal(this, sw);
              xml = sw.toString();
          } catch (Exception e) {
              e.printStackTrace();
          }
          return xml;
      }
docs: Map a Token instance to its XML representation.
  
  @return a String with the description of this object in XML.