protected function _normalizeConfig($orders)
    {
        if (empty($orders)) {
            $orders = [[]];
        } elseif (isset($orders['order']) || isset($orders['callback'])) {
            $orders = [$orders];
        }

        $default = [
            'order' => $this->_table->aliasField($this->_table->getDisplayField()),
            'callback' => null,
        ];

        foreach ($orders as $key => $value) {
            $orders[$key] = $orders[$key] + $default;
        }

        $this->_config = [
            'orders' => $orders,
        ];
    }