code: func (db *dbusImpl) SystemBus() (Connection, error) {
  	if db.systemBus == nil {
  		bus, err := godbus.SystemBus()
  		if err != nil {
  			return nil, err
  		}
  		db.systemBus = &connImpl{bus}
  	}
  
  	return db.systemBus, nil
  }
docs: // SystemBus is part of Interface