Facebook API returning weird String

I'm facing a strange problem right now...

I'm trying to use Facebook API to gather some informations on users on my App, which I can but the returning string is weird..

Here is what I have :

    $params = array("method" => "fql.query",
            "query" => "SELECT first_name, last_name FROM user WHERE uid = $this->userId",
            "callback" => null);

        $result = json_decode($oFbSmarty->getFacebookApi()->api($params));

        $this->setFirstName($result->first_name);
        $this->setLastname($result->last_name);

        var_dump($result);

And here is the result of the var_dump :

string 'null([{"first_name":"Alexandre","last_name":"\u30b4\u30c7\u3093\u30b7\u30aa"}]);' (length=80)

Did someone ever face this ? I can't understand why there is a "null" writtent in the returning string...

Thanks !

EDIT : Well... Actually it's worse than what I thought =/ the "null" part of the response string is here because I didn't fill the "callback" part of the params but put null instead. Doing that makes facebook api automatically return an ready-to-execute string, which means : If I had type "sayPlop" as callback function, returned string would have been =>

"sayPlop(......)"

So if you don't wan't facebook to do that, just don't specify the "callback" parameter, it's optionnal (see Facebook PHP SDK source code).

Thanks !

It looks like it's not passing the JSONP callback, I'm not familiar with the Facebook API but change your $params to this and it will wrap it differently.

$params = array("method" => "fql.query",
            "query" => "SELECT first_name, last_name FROM user WHERE uid = $this->userId",
            "callback" => 'myfunctionname');

I think you must define a function called myfunctionname to process the data.