public static function getTopics(Core $core, $limit = 100, $offset = 0)
 {
     $url = self::getTopicsUrl($core) . "?limit=" . $limit . "&offset=" . $offset;
     $response = Client::GET($url, self::getHeaders($core));
     $body = self::getDataFromResponse($response);
     if (!property_exists($body, "topics")) {
         return null;
     }
     $topics = array();
     foreach ($body->{"topics"} as &$topic) {
         $topics[] = Topic::serializeFromJson($topic);
     }
     return $topics;
 }