Rather than changing the connection string, you can use the IsValidDateTime property of the MySqlDateTime object to help you determine if you can cast the object as a DateTime.
I had a scenario where I was trying to load data from an "UpdateTime" column that was only explicitly set when there was an update to the row (as opposed to the InsertedTime which was always set). For this case, I used the MySqlDataReader.GetMySqlDateTime method like so:
using (MySqlDataReader reader = await MySqlHelper.ExecuteReaderAsync(...))
{
if (await reader.ReadAsync())
{
DateTime? updateTime = reader.GetMySqlDateTime("UpdateTime").IsValidDateTime ? (DateTime?)reader["UpdateTime"] : null;
}
}