protected function doRun()
 {
     $from = $this->getArgumentThreemaId(self::argFrom);
     $secret = $this->getArgument(self::argSecret);
     Common::required($from, $secret);
     //define connection settings
     $settings = new ConnectionSettings($from, $secret);
     //create a connection
     $connector = new Connection($settings, $this->publicKeyStore);
     $result = $connector->credits();
     Common::required($result);
     if ($result->isSuccess()) {
         Common::l("remaining credits: " . $result->getCredits());
     } else {
         Common::e($result->getErrorMessage());
     }
 }