public function getUser($userId)
 {
     $users = $this->getUsers();
     if (!isset($users[$userId])) {
         throw new \InvalidArgumentException('This user does not exist in Slack API');
     }
     return $this->userEntityBuilder->getUser($this->userBuilder->getUser($users[$userId]));
 }
 public function getAll()
 {
     $payload = new UsersListPayload();
     $response = $this->apiClient->send($payload);
     if ($response->isOk()) {
         return array_map(function (User $user) {
             return $this->userBuilder->getUser($user);
         }, $response->getUsers());
     } else {
         throw new SlackApiException($response->getError());
     }
 }