How can i insert NULL values to a database
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when i click on a button it should save the changes i've made to a database, this is the code of the button:

    DataRow drow = sql.ds.Tables["Stagiaire"].NewRow();
            Boolean allowAdd = false;
            if (nom.Text != "" && prenom.Text != "")
                allowAdd = true;
            if (allowAdd)
            {
                drow[1] = imgData;
                drow[2] = nom.Text.ToUpper();
                drow[3] = prenom.Text;
                drow[4] = sexe.SelectedItem.ToString();
                drow[5] = naiss.Text;
                drow[6] = email.Text;
                drow[7] = tele.Text;
                drow[8] = adresse.Text;
                drow[9] = niveau.Text;
                drow[10] = filiere.Text;
                drow[11] = stage.SelectedItem.ToString();
                drow[12] = service.SelectedItem.ToString();
                drow[13] = encadrant.SelectedItem.ToString();
                drow[14] = etablissement.SelectedItem.ToString();
                sql.ds.Tables["Stagiaire"].Rows.Add(drow);
                SqlCommandBuilder cmb = new SqlCommandBuilder(daStagiaire);
                daStagiaire.Update(sql.ds, "Stagiaire");
                XtraMessageBox.Show("Bien Ajouter !");
            }
**My question is : How can i insert NULL values to the database if the text controllers are empty**