public function removeItem($item)
    {
        $nb_index_id = nb_getMixedValue($item, $this->index_field);
        if ((is_numeric($nb_index_id) || nb_isValidGUID($nb_index_id)) && $this->containsKey($nb_index_id)) {
            unset($this->list[$nb_index_id]);
            $this->removeItemIndex($item);
        }
    }