code: func (m *MetadataMapping) Aggregate() MetadataSet {
  	m.RLock()
  	defer m.RUnlock()
  	var set MetadataSet
  	for _, md := range m.mdByName {
  		set = append(set, md)
  	}
  	return set
  }
docs: // Aggregate aggregates all Metadata to a MetadataSet