Object cannot be cast from DBNull to other types.

Question

I am getting issue while tab reach to next new row after loading data from database.

Can anyone please correct the code

private void dataGridSALEITEM_CellValueChanged(object sender, DataGridViewCellEventArgs e) {
 decimal TOTALAMOUNT = 0;
 decimal TOTALCGST = 0;
 decimal TOTALSGST = 0;
 decimal NETTOTAL = 0;
 foreach(DataGridViewRow row in dataGridSALEITEM.Rows) {
  row.Cells[dataGridSALEITEM.Columns[7].Index].Value = (Convert.ToInt32(row.Cells[dataGridSALEITEM.Columns[3].Index].Value) * Convert.ToInt32(row.Cells[dataGridSALEITEM.Columns[4].Index].Value));
  row.Cells[dataGridSALEITEM.Columns[8].Index].Value = (Convert.ToInt32(row.Cells[dataGridSALEITEM.Columns[7].Index].Value) / 200 * Convert.ToInt32(row.Cells[dataGridSALEITEM.Columns[5].Index].Value));
  row.Cells[dataGridSALEITEM.Columns[9].Index].Value = (Convert.ToInt32(row.Cells[dataGridSALEITEM.Columns[7].Index].Value) / 200 * Convert.ToInt32(row.Cells[dataGridSALEITEM.Columns[5].Index].Value));
  row.Cells[dataGridSALEITEM.Columns[10].Index].Value = (Convert.ToInt32(row.Cells[dataGridSALEITEM.Columns[7].Index].Value) + Convert.ToInt32(row.Cells[dataGridSALEITEM.Columns[8].Index].Value) + Convert.ToInt32(row.Cells[dataGridSALEITEM.Columns[9].Index].Value));
  TOTALAMOUNT += Convert.ToDecimal(row.Cells[dataGridSALEITEM.Columns[7].Index].Value);
  TOTALCGST += Convert.ToDecimal(row.Cells[dataGridSALEITEM.Columns[8].Index].Value);
  TOTALSGST += Convert.ToDecimal(row.Cells[dataGridSALEITEM.Columns[9].Index].Value);
  NETTOTAL += Convert.ToDecimal(row.Cells[dataGridSALEITEM.Columns[10].Index].Value);
 }
 txtSUBTOTAL.Text = TOTALAMOUNT.ToString();
 txtCGST.Text = TOTALCGST.ToString();
 txtSGST.Text = TOTALSGST.ToString();
 txtGTOTAL.Text = NETTOTAL.ToString();
}