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