code: public function jsonSerialize()
      {
          $json = [];
  
          if (null !== $this->mediaId) {
              $json['mediaId'] = $this->mediaId;
          }
          if (null !== $this->slide) {
              $json['slide'] = $this->slide;
          }
          if (null !== $this->transition) {
              $json['transition'] = $this->transition;
          }
  
          return $json;
      }
docs: Gets all data that should be available in a json representation.
  
  @return array an associative array of the available variables