presto-main/src/main/java/io/prestosql/operator/aggregation/state/DigestAndPercentileArrayStateFactory.java/GroupedDigestAndPercentileArrayState/setDigest
class GroupedDigestAndPercentileArrayState:        @Override
        public void setDigest(QuantileDigest digest)
        {
            digests.set(getGroupId(), requireNonNull(digest, "digest is null"));
        }