async getMulti(ids, transform) {
    const keys = ids?.map(this.toKey, this);
    const data = await api.get(keys);
    return transform || this.prefix
      ? data::mapEntry(transform, this.toId, this)
      : data;
  }
@param {?string[]} [ids] - if null/absent, the entire storage is returned
@param {function(val:?,key:string):?} [transform]
@return {Promise<?>} - single value or object of id:value