My server returns blank page with 'null' in the corner

Question

I need simple web service to get data from local database, but when I've moved files from test server to actual server I just receive blank page with 'null' in top left corner. My php code is very simple:

<?php
// Include config
require_once 'config/db.php';
$sql = new db();
$conn = $sql->connect();

$task = isset($_GET['task']) ? mysql_real_escape_string($_GET['task']) :  "";

if(!empty($task))
{
    if($task === "totals")
    {
        $qur = mysql_query("working query - no problem here;");
        $result =array();
        while($r = mysql_fetch_array($qur))
        {
            extract($r);
            $result[] = array("total_value" => $total_value, 'orders_date' => $orders_date, 'number_of_orders' => $number_of_orders); 
        }
        $json = $result;
    }
}

@mysql_close($conn);

/* Output header */
header('Content-type: application/json');
echo json_encode($json, JSON_PRETTY_PRINT);
?>

And here is db.php code:

<?php
class db
{
    // Properties
    private $dbhost = 'ip-address';
    private $dbuser = 'xxx';
    private $dbpass = 'yyy';
    private $dbname = 'zzz';
    // Connect
    public function connect()
    {
        $conn = mysql_connect($this->dbhost, $this->dbuser, $this->dbpass);
        mysql_select_db($this->dbname, $conn);
    }
}
?>

Answer 1

May be Json_encode not giving correct answer.

1) Also please make sure JSON_PRETTY_PRINT is only available for PHP versions >= 5.4. It's value is 128, so try replacing JSON_PRETTY_PRINT with 128.

just on error reporting at top of page to debug

2) Also to make sure once try to print $json before encoding it

3) As mentioned in comment just encode only when you are actually getting data

!empty($json){
header('Content-type: application/json');
echo json_encode($json, JSON_PRETTY_PRINT);
}