winform 中向数据库插入空图片是相应的字段值为NULL

Question

这个方法虽然能插入 但数据库中的image 字段值 为 0x  但我想要的image 字段值为NULL  菜鸟求教老鸟呀
            SqlConnection conn = new SqlConnection(@"Server=;DataBase=qkdj;User=sa;Pwd=");
                            conn.Open();
                            SqlCommand cmd = new SqlCommand("insert into qkdj..pbwj_bqy(bkdh,bkmc,nd,qb,op,image1,image2,image3,image4,bz,optime) values('" + textBox18.Text.Trim().ToString() + "','" + label20.Text + "','" + textBox21.Text.Trim().ToString() + "','" + textBox25.Text.Trim().ToString() + "','" + dt.Rows[0]["xm"].ToString() + "',@a,@b,@c,@d,'" + textBox17.Text.Trim().ToString() + "',GETDATE())", conn);
                        
                            byte[] zzz = new byte[Convert.ToInt32(null)];                            if (pictureBox1.Image != null)
                            {
                                FileStream fs = new FileStream(tu1, FileMode.Open, FileAccess.Read);
                                byte[] bytes = new byte[Convert.ToInt32(fs.Length)];
                                fs.Read(bytes, 0, Convert.ToInt32(fs.Length));
                                cmd.Parameters.Add("@a", SqlDbType.Image, (int)fs.Length);
                                cmd.Parameters["@a"].Value = bytes;
                            }
                            else
                            {
                                
                                cmd.Parameters.Add("@a", SqlDbType.Image);
                                cmd.Parameters["@a"].Value = zzz;
                            }
                            if (pictureBox2.Image != null)
                            {
                                FileStream hh = new FileStream(tu2, FileMode.Open, FileAccess.Read);
                                byte[] bbb = new byte[Convert.ToInt32(hh.Length)];
                                hh.Read(bbb, 0, Convert.ToInt32(hh.Length));
                                cmd.Parameters.Add("@b", SqlDbType.Image, (int)hh.Length);
                                cmd.Parameters["@b"].Value = bbb;
                            }
                            else
                            {
                                cmd.Parameters.Add("@b", SqlDbType.Image);
                                cmd.Parameters["@b"].Value = zzz;
                            }

Answer 1

cmd.Parameters["@a"].Value = zzz;=>cmd.Parameters["@a"].Value = null;

Answer 2

图片为空时改成这样试试
cmd.Parameters.Add("@a", SqlDbType.Image);
cmd.Parameters["@a"].Value = DBNull.Value;cmd.Parameters.Add("@b", SqlDbType.Image);
cmd.Parameters["@b"].Value = DBNull.Value;