Please check my code

Dear All, This code is for searching empty cells of certain column. Now I want to search not empty cells of certain column. Please help me.

Here is my code:

if (comboBoxEnterSuspenseAccount.Text != "")

{

con = new OleDbConnection(conString);

var query6 = "SELECT * FROM LalData " +

" WHERE " +

"SuspenseAccount = @suspenceAccount1 " +

"AND[CibtcaNo] = '" + DBNull.Value + "'" +

"AND " +

"(PaymentDate BETWEEN @firstDate AND @lastDate)";

con.Open();

OleDbCommand cmd = new OleDbCommand(query6, con);

cmd.Parameters.AddWithValue("@suspenceAccount6 ", DbType.String).Value = comboBoxEnterSuspenseAccount.Text.ToString();

cmd.Parameters.AddWithValue("@firstDate ", DbType.Date).Value =

dtpFirstDate.Value.ToShortDateString();

cmd.Parameters.AddWithValue("@lastDate ", DbType.Date).Value =

dtpLastDate.Value.ToShortDateString();

adapter = new OleDbDataAdapter(cmd);

adapter.Fill(dt);

dataGridView1.DataSource = dt;

dataGridView1.CurrentCell = dataGridView1.Rows[dataGridView1.Rows.Count - 1].Cells[0];

con.Close();

}