presto-main/src/main/java/io/prestosql/operator/aggregation/ApproximateSetAggregation.java/ApproximateSetAggregation/getOrCreateHyperLogLog
class ApproximateSetAggregation:    private static HyperLogLog getOrCreateHyperLogLog(@AggregationState HyperLogLogState state)
    {
        HyperLogLog hll = state.getHyperLogLog();
        if (hll == null) {
            hll = newHyperLogLog();
            state.setHyperLogLog(hll);
            state.addMemoryUsage(hll.estimatedInMemorySize());
        }
        return hll;
    }