สอบถามเรื่อง Error "Object reference not set to an instance of an object" เกิดขึ้นตอนติดต่อฐ้านข้อมูลครับ

        protected void Page_Load(object sender, EventArgs e)
        {
            try
            {
                clsConnection objConnection = new clsConnection();
                string strSql = "SELECT *FROM A1 ";
                DataSet ds = new DataSet();
                ds = objConnection.ExcuteQuery(strSql, CommandType.Text);
                grdResult.DataSource = ds;
                grdResult.DataBind();
            }
            catch (Exception ex)
            {
                Response.Write(ex.Message);
            }
        }

*----------------------------------------- class clsConnection -------------------------------------------------------*
    public class clsConnection
    {
        private string strConection = WebConfigurationManager.ConnectionStrings["ConnectionSQL"].ConnectionString;
        private SqlConnection myConnection;
        private SqlCommand myCommand;
        private SqlDataAdapter myDataAdapter;


        private void OpenConnection()
        {
            try
            {
                if (myConnection == null)
                {
                    myConnection = new SqlConnection();
                    myConnection.ConnectionString = strConection;
                    myConnection.Open();
                }
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }

        public DataSet ExcuteQuery(string strText,
                                   CommandType cmdType)
        {
            try
            {
                OpenConnection();
                myDataAdapter = new SqlDataAdapter();
                myDataAdapter.SelectCommand = myCommand; // <======= Object reference not set to an instance of an object.
                myDataAdapter.SelectCommand.Connection = myConnection;
                myDataAdapter.SelectCommand.CommandType = cmdType;
                myDataAdapter.SelectCommand.CommandText = strText;
                DataSet ds = new DataSet();
                myDataAdapter.Fill(ds);
                return ds;
            }
            catch(Exception ex)
            {
                throw ex;
            }
        }

    }