Cannot get thumbnail in rss feed in laravel

I am using willvincent feed reader to parse rss feeds, But i cannot seem to get the thumbail of the images,Here is my code

Route::get('feed', function(Request $request) {    $f = FeedsFacade::make('http://www.cbn.com/cbnnews/us/feed/');    // $results = [    //     'image' => $f->get_image_url(),    // ];    foreach($f->get_items(0, $f->get_item_quantity()) as $item) {        $i['title'] = $item->get_title();        $i['thumbnail'] = $item->get_thumbnail();        $i['description'] = $item->get_description();        $i['content'] = $item->get_content();        $i['link'] = $item->get_link();        $i['date'] = $item->get_date();        $results['items'][] = $i;    }    dd($results);})->name('feed');

Thumbnail always return null, will appreciate anyone's help