code: protected String resource_to_string(nitro_service service, options option)
  	{
  		String onerror = service.get_onerror();
  		return service.get_payload_formatter().resource_to_string(this, option, onerror);
  	}
docs: Converts MPS resource to Json string.
  @param service nitro_service object.
  @param option Options object.
  @return  string in Json format.