public function get($index = 0)
    {

        if (is_int($index)) {
            if ($index + 1 > $this->count()) {
                return null;
            } else {
                return current(array_slice($this->_items, $index, 1));
            }
        } else {

            if ($index instanceof \MongoId) {
                $index = (string) $index;
            }

            if ($this->has($index)) {
                return $this->_items[$index];
            }
        }

        return null;
    }