public function setFiles($files = array())
    {
        if (count($files) === 0) {
            $this->_files = $_FILES;
        } else {
            $this->_files = $files;
        }

        foreach($this->_files as $file => $content) {
            if (!isset($content['error'])) {
                unset($this->_files[$file]);
            }
        }

        return $this;
    }