code: func (s *StanServer) setLastError(err error) {
  	s.mu.Lock()
  	s.lastError = err
  	s.state = Failed
  	s.mu.Unlock()
  	s.log.Fatalf("%v", err)
  }
docs: // setLastError sets the last fatal error that occurred. This is
  // used in case of an async error that cannot directly be reported
  // to the user.