presto-main/src/main/java/io/prestosql/type/setdigest/MergeSetDigestAggregation.java/MergeSetDigestAggregation/combine
class MergeSetDigestAggregation:    @CombineFunction
    public static void combine(SetDigestState state, SetDigestState otherState)
    {
        merge(state, otherState.getDigest());
    }