在linux服务器上的非对象上调用成员函数fetch_assoc(），但在windows上则不然

当我在linux服务器上运行这个页面时，我会收到上面的错误，但当我在windows机器上运行它时，它不会给我任何错误。以下是我的脚本：

include_once '/../src/init.php';
$userid = $user_data['userid'];
$date = ('Y-m-d'); //get todays date from the server

$db = new mysqli('localhost', 'root', '', 'logfile');
if ($db->connect_error) {

   $error = $db->connect_error;
} else {
$sql = "SELECT a.kiloLogid,a.travelDate,a.openning, a.closing, a.clientsName,a.timeIn,a.timeOut, a.destination,a.diff
                FROM viewDailyDiff a
                WHERE a.`userid` = $userid AND a.`travelDate` = '".$date."'";
$result = $db->query($sql);
if ($db->error) {
    $error = $db->error;
}
}



function getRow($result)
{
 return $result->fetch_assoc();  //the error is on this line
}

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