presto-main/src/main/java/io/prestosql/operator/aggregation/state/DigestAndPercentileStateFactory.java/DigestAndPercentileStateFactory/getGroupedStateClass
class DigestAndPercentileStateFactory:    @Override
    public Class<? extends DigestAndPercentileState> getGroupedStateClass()
    {
        return GroupedDigestAndPercentileState.class;
    }