presto-main/src/main/java/io/prestosql/operator/aggregation/DoubleCorrelationAggregation.java/DoubleCorrelationAggregation/combine
class DoubleCorrelationAggregation:    @CombineFunction
    public static void combine(@AggregationState CorrelationState state, @AggregationState CorrelationState otherState)
    {
        mergeCorrelationState(state, otherState);
    }