code: func (m *messagePageIterator) Next(ctx context.Context) (*MessagePage, error) {
  	mp := new(MessagePage)
  	err := m.p.Next(ctx, mp)
  	if err != nil {
  		return nil, err
  	}
  	m.p.SetNextPageURI(mp.NextPageURI)
  	return mp, nil
  }
docs: // Next returns the next page of resources. If there are no more resources,
  // NoMoreResults is returned.