protected function getFiles()
    {
        if (!$this->files) {
            $files = array();
            if ($this->batch) {
                $files = $this->batch->getSessionVariable('files');
            } else {
                $files = $this->_session->files;
            }
            if (!is_array($files)) {
                $files = array();
            }
            $this->files = $files;
        }
        return $this->files;
    }