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