code: protected function finish($output = null)
      {
          if (! is_null($output)) {
              $file = fopen($this->file, 'w+');
              fwrite($file, $output);
              fclose($file);
              return $output;
          }
  
          return false;
      }
docs: Finish cache and save file
  
  @param string $output
  
  @return mixed