public Set<DocumentId> documentIds() {
        return exceptions.stream()
                .filter(e -> e.documentId().isPresent())
                .map(e -> e.documentId().get())
                .collect(Collectors.toSet());
    }
Aggregates multiple instances of {@link FeedException}

@author bjorncs
vespa-feed-client-api/src/main/java/ai/vespa/feed/client/MultiFeedException.java