public function toNestedArray()
    {
        $result = [];

        foreach ($this->items as $item) {
            if (is_object($item)) {
                if (method_exists($item, 'toMap')) {
                    $result[] = $item->toMap();
                } else {
                    $result[] = (array) $item;
                }
            } else {
                $result[] = $item;
            }
        }

        return $result;
    }