code: public function execute($command, callable $next)
      {
          if (!($command instanceof TransferObjectCommand)) {
              return $next($command);
          }
  
          $object = $command->getPayload();
  
          $this->validator->validate($object);
  
          return $next($command);
      }
docs: @param mixed    $command
  @param callable $next
  
  @return mixed