public function __construct(array $args = [])
 {
     $this->args = $args;
     if (!isset($args['client'])) {
         $this->args['client'] = static function () {
             static $handler;
             if (!$handler) {
                 $handler = Client::getDefaultHandler();
             }
             return new Client(['handler' => $handler]);
         };
     }
 }