code: func (n *NetStore) getFetcher(ref Address) *fetcher {
  	key := hex.EncodeToString(ref)
  	f, ok := n.fetchers.Get(key)
  	if ok {
  		return f.(*fetcher)
  	}
  	return nil
  }
docs: // getFetcher retrieves the fetcher for the given address from the fetchers cache if it exists,
  // otherwise it returns nil