docs: public T xpath(String expression, String value) {
          if (xpathMessageConstructionInterceptor == null) {
              xpathMessageConstructionInterceptor = new XpathMessageConstructionInterceptor();
  
              if (getAction().getMessageBuilder() != null) {
                  (getAction().getMessageBuilder()).add(xpathMessageConstructionInterceptor);
              } else {
                  PayloadTemplateMessageBuilder messageBuilder = new PayloadTemplateMessageBuilder();
                  messageBuilder.getMessageInterceptors().add(xpathMessageConstructionInterceptor);
  
                  getAction().setMessageBuilder(messageBuilder);
              }
          }
  
          xpathMessageConstructionInterceptor.getXPathExpressions().put(expression, value);
          return self;
      }