Handle Null Values from DB in Asp.net Web API with Oracle DB On HTTP GET

Question

I am trying to GET all values from a Oracle Table using a web api.

The Get works fine when there are no null values for columns in oracle table

but returns a http 500 when any of the columns are null in the table. Is there a way to handle this without using a procedure? Below is the method I am using would like to keep the logic same if possible. Any suggestions are appreciated.

[HttpGet]
        [ActionName("GetData")]
        public object Get()
        {
            List<SelectData> TestList = new List<SelectData>();
            string connStr = ConfigurationManager.AppSettings.Get("ConnStr");

            using (var conn = new OracleConnection(connStr))
            {
                conn.Open();
                OracleCommand cmd = new OracleCommand();
                cmd.CommandText = "select * from DB_DATA";
                cmd.Connection = conn;
                OracleDataReader dr = cmd.ExecuteReader();
                SelectData ListObject = new SelectData();

                while (dr.Read())
                {
                   //Error if any of these are null

                    ListObject.DATA_ID = dr.GetInt32(0);                   
                    ListObject.Name = dr.GetString(1);
                    ListObject.LastName = dr.GetString(2);
                    ListObject.COMMENTS = dr.GetString(3);
                    ListObject.Address = dr.GetString(4);

                    TestList.Add(ListObject);
                }
                conn.Close();
            }
            return TestList;
        }