ZipArchive :: addEmptyDir不是在ubuntu 3.15和PHP 5.3.10中创建空目录

I'm trying to add empty director to archive, by using the following code in ubuntu3.15 running PHP 5.3.10. But it is creating a zip without empty directory in it. Any idea what's wrong in the code?

$zip = new ZipArchive();
$filename = "/var/www/enteliweb/website/public/test.zip";

if ($zip->open($filename, ZipArchive::CREATE)!==TRUE) 
  {
    exit("cannot open <$filename>
");
  }

if($zip->addEmptyDir('newDirectory')) 
  {
    echo 'Created a new root directory';
  } else {
    echo 'Could not create the directory';
  }
$zip->close();