private function render()
    {
        add_action('admin_notices', function () {
            if (is_array($this->message) && !empty($this->message)) {
                echo '<div class="error notice">';
                echo '<ul>';
                foreach ($this->message as $message) {
                    echo '<li>' . $message . '</li>';
                }
                echo '</ul>';
                echo '</div>';

                $this->message = array();
            }
        });
    }