Anyone have a solution how to save datagridview data to mysql and retrive it (with aes_encrypt/decrypt)

Question

this code is that what i have now and it works but i become always this message. the image is in german sorry for that google translated:

the object reference was not set to an object instance

the problem comes when i click the Populate function (in visualstudio is no errormessage only in the tool)

thank you guys

Error Message

private void Add(string Kundenname, string Game, string Bezahlung, string Bezahlt, string Erledigt, string PayPalEmail, string ACCEmail, string ACCPW)
    {
        //SQL STMT
        string sql = "INSERT INTO kunden(Kundenname,Game,Bezahlung,Bezahlt,Erledigt,PayPalEmail,ACCEmail,ACCPW) VALUES(@KUNDENNAME,@GAME,@BEZAHLUNG" +
            ",@BEZAHLT,@ERLEDIGT,@PAYPALEMAIL,@ACCEMAIL,@ACCPW)";
        cmd = new MySqlCommand(sql, con);
        //ADD PARAMETERS
        cmd.Parameters.AddWithValue("@KUNDENNAME", Kundenname);
        cmd.Parameters.AddWithValue("@GAME", Game);
        cmd.Parameters.AddWithValue("@BEZAHLUNG", Bezahlung);
        cmd.Parameters.AddWithValue("@BEZAHLT", Bezahlt);
        cmd.Parameters.AddWithValue("@ERLEDIGT", Erledigt);
        cmd.Parameters.AddWithValue("@PAYPALEMAIL", PayPalEmail);
        cmd.Parameters.AddWithValue("@ACCEMAIL", ACCEmail);
        cmd.Parameters.AddWithValue("@ACCPW", Encrypt(ACCPW));
        //OPEN CON AND EXEC insert
        try
        {
            con.Open();
            if (cmd.ExecuteNonQuery() > 0)
            {
                ClearTxts();
                MessageBox.Show("Successfully Inserted");
            }
            con.Close();
            Retrieve();
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
            con.Close();
        }
    }

    private void Populate(String ID, string Kundenname, string Game, string Bezahlung, string Bezahlt, string Erledigt, string PayPalEmail, string ACCEmail, string ACCPW)
    {
        dgv.Rows.Add(ID, Kundenname, Game, Bezahlung, Bezahlt, Erledigt, PayPalEmail, ACCEmail, ACCPW);
    }
    //RETRIEVE FROM DB
    private void Retrieve()
    {
        dgv.Rows.Clear();
        //SQL STMT
        string sql = "SELECT * FROM kunden ";
        cmd = new MySqlCommand(sql, con);
        //OPEN CON,RETRIEVE,FILL DGVIEW
        try
        {
            con.Open();
            adapter = new MySqlDataAdapter(cmd);
            adapter.Fill(dt);
            //LOOP THRU DT
            foreach (DataRow row in dt.Rows)

            {
                    Populate(row[0].ToString(), row[1].ToString(), row[2].ToString(), row[3].ToString(), row[4].ToString(), row[5].ToString(), row[6].ToString(), row[7].ToString(), row[8].ToString());
                foreach (DataGridViewRow rows in dgv.Rows)
                {
                     rows.Cells[8].Value = Decrypt(rows.Cells[8].Value.ToString());
                }
            }
                con.Close();
                //CLEAR DT
                dt.Rows.Clear();
            }

        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
            con.Close();
        }
    }