code: func (h HeartbeatMode) CheckAndSetDefaults() error {
  	switch h {
  	case HeartbeatModeNode, HeartbeatModeProxy, HeartbeatModeAuth:
  		return nil
  	default:
  		return trace.BadParameter("unrecognized mode")
  	}
  }
docs: // CheckAndSetDefaults checks values and sets defaults