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