C# Check if SQLDataReader has field or field is null

Check if SQLDataReader has field or field is null

// assumes dr is a SqlDataReader

            List<string> columns_ = GetColumns(dr);

            if (columns_.IndexOf("MissingField") == -1) { throw new Exception("Query did not contain \"MissingField\""); }
            this.DBID = (int)dr["ID"];
            this.Created = (DateTime)dr["Created"];
            this.DataText = (string)dr["MissingField"];
            if (!dr.IsDBNull(columns_.IndexOf("MsgType")) { this.MsgType = (string)dr["MsgType"]; }


            if (!dr.IsDBNull(columns_.IndexOf("MsgDriver")) { this.MsgDriver = (int)dr["MsgDriver"]; }
            if (!dr.IsDBNull(columns_.IndexOf("MsgJob")) { this.MsgDriver = (int)dr["MsgJob"]; }
        }


        public List<string> AllColumnNames(SqlDataReader dr)
        {
            List<string> res = new List<string>();
            for (int i = 0; i < dr.FieldCount; i++)
            {
                res.Add(dr.GetName(i));
            }
            return res;
        }