code: func (s *GraphQuery_Search) Normalize() error {
  	// for now, start and end MUST be timestamp values.
  	switch s.Start.Value.(type) {
  	case *PropertyValue_Time:
  	default:
  		return fmt.Errorf("invalid Start type: %T", s.Start.Value)
  	}
  	switch s.End.Value.(type) {
  	case *PropertyValue_Time:
  	default:
  		return fmt.Errorf("invalid End type: %T", s.End.Value)
  	}
  	return nil
  }
docs: // Normalize returns nil iff this Search is in a bad state.