Facebook php SDK v4.0 codeigniter

I integrated facebook php v4.0 in codeigniter. In localhost, Pages are loading all fine and also I can get redirect url. But when I take site to online. Site opens blank without any error. Then I unload facebook library from controller and pages load correctly. I think its problem with facebook library. Below is my facebook library :

<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');
if ( session_status() == PHP_SESSION_NONE ) {
session_start();
}
// Autoload the required files
require_once( APPPATH . 'libraries/facebook/vendor/autoload.php' );
require_once( APPPATH . 'libraries/Facebook/HttpClients/FacebookHttpable.php' );
require_once( APPPATH . 'libraries/Facebook/HttpClients/FacebookCurl.php' );
require_once( APPPATH . 'libraries/Facebook/HttpClients/FacebookCurlHttpClient.php' );

require_once( APPPATH . 'libraries/Facebook/Entities/AccessToken.php' );
require_once( APPPATH . 'libraries/Facebook/Entities/SignedRequest.php' );

require_once( APPPATH . 'libraries/Facebook/FacebookSession.php' );
require_once( APPPATH . 'libraries/Facebook/FacebookRedirectLoginHelper.php' );
require_once( APPPATH . 'libraries/Facebook/FacebookSignedRequestFromInputHelper.php' );
require_once( APPPATH . 'libraries/Facebook/FacebookJavaScriptLoginHelper.php' );

require_once( APPPATH . 'libraries/Facebook/FacebookRequest.php' );
require_once( APPPATH . 'libraries/Facebook/FacebookResponse.php' );
require_once( APPPATH . 'libraries/Facebook/FacebookSDKException.php' );
require_once( APPPATH . 'libraries/Facebook/FacebookRequestException.php' );
require_once( APPPATH . 'libraries/Facebook/FacebookOtherException.php' );
require_once( APPPATH . 'libraries/Facebook/FacebookAuthorizationException.php' );
require_once( APPPATH . 'libraries/Facebook/GraphObject.php' );
require_once( APPPATH . 'libraries/Facebook/GraphSessionInfo.php' );

use Facebook\FacebookRedirectLoginHelper;
use Facebook\FacebookSession;
use Facebook\FacebookRequest;
class Facebook {
var $ci;
var $helper;
var $session;
var $permissions;
public function __construct() {
$this->ci =& get_instance();
$this->permissions = $this->ci->config->item('permissions', 'facebook');
// Initialize the SDK
        
FacebookSession::setDefaultApplication( $this->ci->config->item('api_id', 'facebook'), $this->ci->config->item('app_secret', 'facebook') );
// Create the login helper and replace REDIRECT_URI with your URL
// Use the same domain you set for the apps 'App Domains'
// e.g. $helper = new FacebookRedirectLoginHelper( 'http://ift.tt/1Nh2HWx' );
$this->helper = new FacebookRedirectLoginHelper( $this->ci->config->item('redirect_url', 'facebook') );

if ( $this->ci->session->userdata('fb_token') ) {
$this->session = new FacebookSession( $this->ci->session->userdata('fb_token') );
// Validate the access_token to make sure it's still valid
try {
if ( ! $this->session->validate() ) {
$this->session = null;
}
} catch ( Exception $e ) {
// Catch any exceptions
$this->session = null;
}
} else {
// No session exists
try {
$this->session = $this->helper->getSessionFromRedirect();
} catch( FacebookRequestException $ex ) {
// When Facebook returns an error
} catch( Exception $ex ) {
// When validation fails or other local issues
}
}
if ( $this->session ) {
  
$this->ci->session->set_userdata( 'fb_token', $this->session->getToken() );
$this->session = new FacebookSession( $this->session->getToken() );
}
}
/**
* Returns the login URL.
*/
public function login_url() {
return $this->helper->getLoginUrl( $this->permissions );
}
/**
* Returns the current user's info as an array.
*/
public function get_user() {
if ( $this->session ) {
/**
* Retrieve User’s Profile Information
*/
// Graph API to request user data
$request = ( new FacebookRequest( $this->session, 'GET', '/me' ) )->execute();
// Get response as an array
$user = $request->getGraphObject()->asArray();
return $user;
}
return false;
}
}