菜鸟求教~ System.NullReferenceException: 未将对象引用设置到对象的实例。

Question

异常详细信息: System.NullReferenceException: 未将对象引用设置到对象的实例。源错误: 
他说这行错误 System.Data.SqlClient.SqlParameter[] para = 
            { 
                new SqlParameter("@title",book.Title),
                new SqlParameter("@author",book.Author),
                new SqlParameter("@publisherId",book.Publisher.Id),
                new SqlParameter("@publishDate",book.PublishDate),
                new SqlParameter("@ISBN",book.Isbn),
                new SqlParameter("@wordsCount",book.WordsCount),
                new SqlParameter("@unitPrice",book.UnitPrice),
                new SqlParameter("@contentDescription",book.ContentDescription),
                new SqlParameter("@authorDescription",book.AuthorDescription),
                new SqlParameter("@editorComment",book.EditorComment),
                new SqlParameter("@TOC",book.Toc),
                new SqlParameter("@categoryId",book.Category.Id),
                new SqlParameter("@clicks",book.Clicks)
            };
求教这是为什么

Answer 1

可能是book或book.Publisher或book.Category为空，调试一下看看

Answer 2

他再NEW那行就报错了 根本不执行下面的
我用的是DetailsView里的修改 绑定对象数据源时候出的这个毛病