Im trying to get a value once I click on a checkbox for a custom DataGrid view filled with a SQL query. The idea its to build a list of selected items with the value ID_COMANDA to delete later

Now I dont know why Im getting a null exceptcion error. I tried to set it via data building it just dosent work

This is the funtion that sets data into the data grid

private void ComandasProcesadas(Mesas mesa_seleccionada)
 {


     // Fetch the data
     List<Comanda> comandas_procesadas = Database.GetComandasActivas(mesa_seleccionada.ID_MESA);

     // Set the AutoGenerateColumns property to false
     COMANDAS_PROCESADAS.AutoGenerateColumns = false;
     // Handle the CellPainting event to draw a larger checkbox
     COMANDAS_PROCESADAS.CellPainting += new DataGridViewCellPaintingEventHandler(COMANDAS_PROCESADAS_CellPainting);

    

     COMANDAS_PROCESADAS.CellContentClick += DataGridView_CellContentClick;

    // Add the DataGridView to the form's controls
    // this.Controls.Add(COMANDAS_PROCESADAS);

     // Clear existing rows and set DataSource
     COMANDAS_PROCESADAS.Rows.Clear();
     COMANDAS_PROCESADAS.DataSource = comandas_procesadas;

     
   
 }

This is the SQL query and data binding

while (reader.Read())
{
  
    var comanda = new Comanda
    {
        ID_COMANDA = Convert.ToInt32(reader["ID_COMANDA"]),
        NUM_COMANDA = Convert.ToInt32(reader["NUM_COMANDA"]),
        CANTIDAD = Convert.ToDecimal(reader["CANTIDAD"]),
        ITEM = reader["ITEM"].ToString(),
        TOTAL = Convert.ToDecimal(reader["TOTAL"]),
        NOTAS = reader["NOTAS"].ToString(),
        NOMBRE_SALONERO = reader["NOMBRE_SALONERO"].ToString(),
        FECHA = reader["FECHA"].ToString(),
        TIEMPO_COMANDA = CalculateDifference(reader["FECHA"].ToString(), reader["HORA_INICIO"].ToString()),
        IsNote = false // Regular row

       
    };
    Console.WriteLine(comanda.ToString());
    comandas_procesadas.Add(comanda);
}

I dont know why Im failing. Any help is appreciated.

Thanks in advance !

Create a list of selected items