The Api.php isn't working

In app/Api.php, the curl call does not work, it returns something empty, the issue is there:

static function get($url) {
    $curl = curl_init();
    $url = API_BASE . $url . "/?format=json";
    curl_setopt($curl, CURLOPT_URL, $url);
    curl_setopt($curl, CURLOPT_HTTPHEADER, array('Content-type: application/json'));
    curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
    $result = curl_exec($curl);
    curl_close($curl);
    return $result;
}