How to close DB

Im using connect-domain to handle the errors for DB connection. When no data is found in DB, connect-domain throws the error. Below is the code

db.store.find({'_id':id},function (err, data) {
        if (err) {
            throw new Error("error");
        }
        else if (data == null) {
            throw new Error("data not present in DB");
            // DB connection close
        }
        else
        {
        console.log(data);
        });

But I want DB connection also to be closed when such errors occur.

Any help on this will be really helpful.

Thanks,