docs: public IUnmarshallingContext getUnmarshaller(String packageName, String bindingName) throws JiBXException
      {
          JIBXContextHolder jAXBContextHolder = this.get(packageName, bindingName);
          if (jAXBContextHolder == null)
              return null;    // Never
          return jAXBContextHolder.getUnmarshaller();
      }