empty cell in datagridview

if (dataGridView2.Columns[e.ColumnIndex].Name == "ColumnName")
        {
            if (String.IsNullOrEmpty(e.FormattedValue.ToString()))
            {
                dataGridView1.Rows[e.RowIndex].ErrorText =
                    "Column Name must not be empty";
                e.Cancel = true;
            }
        }

foreach (DataGridViewRow rw in this.dataGridView2.Rows)
{
  for (int i = 0; i < rw.Cells.Count; i++)
  {
    if (rw.Cells[i].Value == null || rw.Cells[i].Value == DBNull.Value || String.IsNullOrWhitespace(rw.Cells[i].Value.ToString())
    {
      // Do your stuff...
    }
  }
}