return s.Label.Empty() && s.Field.Empty()
}

// For any index defined by IndexFields, if a matcher can match only (a subset)
// of objects that return <value> for a given index, a pair (<index name>, <value>)
// wil be returned.
func (s *SelectionPredicate) MatcherIndex(ctx context.Context) []MatchValue {
	var result []MatchValue
	for _, field := range s.IndexFields {
		if value, ok := s.Field.RequiresExactMatch(field); ok {