FQL没有返回任何内容

I'm trying to get:

• likes count of page
• posts count of page
• posts likes count of page

I'm using the following PHP script:

<?php
# Error Printing
ini_set('display_errors',1);
ini_set('display_startup_errors',1);
error_reporting(-1);

require_once('FacebookAPI/Facebook.php');
$facebook = new Facebook(array(
'appId'  => 'xxxxxxxxxxxxxx',
'secret' => 'yyyyyyyyyyyyyy',
));

# Get User ID
$user = $facebook->getUser();
$fql  = "SELECT like_info.like_count, comment_info.comment_count, share_count, post_id
         FROM stream 
         WHERE source_id = 'PAGE_ID'";
$param  =   array(
                  'method'    => 'fql.query',
                  'query'     => $fql,
                  'callback'  => ''
                  );
$fqlResult   =   $facebook->api($param);
$asset_count = 0;
foreach($fqlResult as $row){
    $asset_count += (int)$row['like_info.like_count'] + (int)$row['comment_info.comment_count']+ (int)$row['share_count']+ (int)$row['post_id'];               
}
echo "<br/><br/>";
echo $asset_count;
?>

But it's returning a blank screen, what's wrong with it?
It's not printing any errors either, although I enabled error logging/printing:

ini_set('display_errors',1);
ini_set('display_startup_errors',1);
error_reporting(-1);