return union(knownCurrentValueSnapshots, valueSnapshots);
        }

        @Override
        public ImmutableSortedMap<String, CurrentFileCollectionFingerprint> getFileFingerprints() {
            return fileFingerprints;
        }

        @Override
        public ImmutableSortedMap<String, CurrentFileCollectionFingerprint> getAllFileFingerprints() {

            hasher.putString(entry.getKey());
            entry.getValue().appendToHasher(hasher);
        }
        for (Map.Entry<String, CurrentFileCollectionFingerprint> entry : result.getFileFingerprints().entrySet()) {
            hasher.putString(entry.getKey());
            hasher.putHash(entry.getValue().getHash());
        }
    }