"no records found" not showing

@mitha

If search returns no data "no records found" message is not showing.How can i get it .I have 4 columns in my data table. if no value is found in database i return $row[] = array();
$output = array(
"draw" => $this->input->get_post('draw'),
"recordsTotal" => $totalNum,
"recordsFiltered" => $totalFilter,
"data" => $row
);
But the message is not showing.