code: public function getCustomFields($parameters=array())
      {
          $this->_harvest = $this->_harvestHelper->parse('getCustomFields', $parameters);
          if (!array_key_exists('id', $parameters)) $this->_harvest['url'] = $this->_harvest['url'] . '/';
          $this->sendRequest();
      }
docs: It is explicitely required to do custom field here because we require the trailing slash, because
  in this case Sinatra didn't give us an option not to.