code: protected function _pushError($resource, $code, $title, $message = '')
      {
          $this->_errors[] = [
              'code'      => $code,
              'message'   => $message,
              'resource'  => $resource,
              'title'     => $title,
          ];
  
          return $this;
      }
docs: All error objects have field and code properties so that your client
  can tell what the problem is.
  
  If resources have custom validation errors, they should be documented
  with the resource.
  
  @param string $resource The erroneous resource
  @param string $code
  @param string $title A title for the error
  @param string $message A friendly message
  @return self