code: public function renderRichResponseItem()
      {
          $out = [];
          $simpleResponse = [];
  
          if ($this->ssml) {
              $simpleResponse['ssml'] = $this->ssml;
          }
  
          if ($this->displayText) {
              $simpleResponse['displayText'] = $this->displayText;
          }
  
          if ($this->textToSpeech) {
              $simpleResponse['textToSpeech'] = $this->textToSpeech;
          }
  
          $out['simpleResponse'] = $simpleResponse;
  
          return $out;
      }
docs: Render a single Rich Response item as array.
  
  @return null|array