PHP JSON array_push用空格替换NULLS？

Hi guys I am using the array_Push function and I am wondering if there's any way for the array_push function to return

                array_push($result, array('order_id' => $row[0],
                                  'type'  => $row[2],
                                  'description' => nl2br($row[3]),
                                  'amount' => $row[4],
                                  ));

and with the json_encode i get

   "result":[{"order_id":"67","type":"HEADER","description":"Coca Cola","amount":null},{"order_id":"72","type":"TEXT","description":"French Fries","amount":null}

this is output in a table as

    $.each(data.result, function(){
        $("tbody").append("<tr id='order_"+this['order_id']+"'><td>"+this['type']+"</td><td></td><td>"+this['description']+" </td><td>"+this['amount']+"</td><br>");

So i was wondering if there is a way for the NULL values to be returned as blanks instead? IF so, where can I do this?

Just do

'amount' => (is_null($row[4]) ? '' : $row[4])

foreach($row as &$value){   
    $value = $value === null ? '' : $value;
}