Cart user info and shipping info cleanup using Javascript SDK

We are trying to implement user info auto-fill and shipping info using JavaScript SDK. Info fill works well ( overall info and shipping info), but after user logout in OUR system, we need to cleanup all the data from cart, keeping cart items in place. We cannot find method or way to clean those, since values are required and cannot be null.

We are interested how cleanup of user’s data in cart could be achieved, or maybe we are generally doing something wrong.

Looking forward to get some help, thanks !