code: public function getIsExistAsync(Requests\GetIsExistRequest $request) 
      {
          return $this->getIsExistAsyncWithHttpInfo($request)
              ->then(
                  function ($response) {
                      return $response[0];
                  }
              );
      }
docs: /*
  Operation getIsExistAsync
  
  Check if a specific file or folder exists
  
  @param Requests\GetIsExistRequest $request is a request object for operation
  
  @throws \InvalidArgumentException
  @return \GuzzleHttp\Promise\PromiseInterface