presto-main/src/main/java/io/prestosql/operator/scalar/HyperLogLogFunctions.java/HyperLogLogFunctions/emptyApproxSet
class HyperLogLogFunctions:    @ScalarFunction
    @Description("an empty HyperLogLog instance")
    @SqlType(StandardTypes.HYPER_LOG_LOG)
    public static Slice emptyApproxSet()
    {
        return ApproximateSetAggregation.newHyperLogLog().serialize();
    }