code: func (s *BufferStore) SaveTo(m Mutator) error {
  	err := s.WalkBuffer(func(k Key, v []byte) error {
  		if len(v) == 0 {
  			return m.Delete(k)
  		}
  		return m.Set(k, v)
  	})
  	return err
  }
docs: // SaveTo saves all buffered kv pairs into a Mutator.