public Book GetBook(Guid id)
        {
            var session = OpContext.OpenSystemSession();
            var bk      = session.GetEntity <IBook>(id);

            if (bk == null)
            {
                OpContext.WebContext.SetResponse(status: HttpStatusCode.NotFound);
                return(null);
            }
            return(bk.ToModel(details: true));
        }