用linq做datatable分组统计时，字段为null 转换类型出错的解决方案 亲测

    var query = from t in dt_hr.AsEnumerable()

                        group t by new { t1 = t.Field<string>("f3") } into m
                        select new
                        {
                            empno = m.Key.t1,

                            sum__finace = m.Sum(t => t[15] != DBNull.Value ? Convert.ToDouble(t[15]) : 0.00),

                            sum__real = m.Sum(t => t[16] != DBNull.Value ? Convert.ToDouble(t[16]) : 0.00)

                        };

            foreach (var item in query.ToList())
            {
                if (item.sum__finace == 1.01 || item.sum__finace == 0.99)
                {
                   MessageBox.Show("hello hill");
                }

            }