code: func (p *objectWalker) walkAllRefs() error {
  	// Walk over all the references in the repo.
  	it, err := p.Storer.IterReferences()
  	if err != nil {
  		return err
  	}
  	defer it.Close()
  	err = it.ForEach(func(ref *plumbing.Reference) error {
  		// Exit this iteration early for non-hash references.
  		if ref.Type() != plumbing.HashReference {
  			return nil
  		}
  		return p.walkObjectTree(ref.Hash())
  	})
  	return err
  }
docs: // walkAllRefs walks all (hash) refererences from the repo.