code: public String param(String name) throws MissingParam {
          String ret = routeResult.pathParams().get(name);
          if (ret != null) {
              return ret;
          }
  
          if (bodyParams != null && bodyParams.containsKey(name)) {
              return bodyParams.get(name).get(0);
          }
  
          ret = routeResult.queryParam(name);
          if (ret != null) {
              return ret;
          }
  
          throw new MissingParam(name);
      }
docs: Order: path, body, query
  
  <p>When there's no param, this method will throw exception <code>MissingParam</code>.
  If you don't handle this exception, response "400 Bad Request" will be automatically
  responded by method respondMissingParam (you can override it if you want).
  If you want "null" instead, please use method "paramo".