query_method from mysql to mysqli

<?php
require_once 'connect.php';

function query_method($db = null, $sql = null)
{
    //if ($result = $db->query("SELECT * FROM permissions")) {
    if ($result = $db->query($sql))
    {
        return ($db == null || $sql == null)?false:$result;
    }
}

$result = query_method($db ,"SELECT * FROM permissions");

if($result->num_rows)
{
    echo '<pre>';
    while($row = $result->fetch_object())
    {
        echo '<pre>';
        print_r($row);
        echo '</pre>';
    }
}
?>