Group.getInfo doesn't return main_photo, get photo by id?

Question

API

Unable to get photo using main_photo. Why are there pitfalls everywhere, why is everything so poorly documented, why don’t you take it, it doesn’t work.
It turns out that the photo (url) needs to be extracted using photo_id ? If so, why is the main_photo field needed then???

OKSDK.REST.call("group.getInfo", {uids: groupId, fields : "name, location_id, main_photo,city, photo_id," +
    "admin_id, description, country, access_type"},
        function(status, data, error) {

            if(status == 'ok')
            {
                console.log(data);
                console.log(data[0].name);
                console.log(data[0].main_photo);
            }
            else
            {

            }

        });