如果var类型的变量或对象为null，那么如何为其赋值

Question

我想要做的是，如果row为null，那么如何编程为其分配一个新行

var row = (from obj in _objdb.tbl123 where obj.cus_id == hidCusRowId.Value select obj).ToList();

                    if (row == null)
                    {
                        DataTable dt = new DataTable();
                        DataRow dr = dt.NewRow();

                        TextBox objtxt = this.Master.FindControl("ContentPlaceHolder1").FindControl("txt0" ) as TextBox;
                        TextBox objtxtsize = this.Master.FindControl("ContentPlaceHolder1").FindControl("txts0") as TextBox;

                        dt.Columns.Add(objtxt.Text);
                        dr[0] = objtxtsize.Text;
                        List<string> lt = new List<string>();
                        lt.Add(objtxtsize.Text);
                        row.Add(lt.ToList());
                    }

                    GridView1.DataSource = row;
                    GridView1.DataBind();

在row.add（lt.ToList（））....

上发生错误