presto-main/src/main/java/io/prestosql/operator/aggregation/ReduceAggregationFunction.java/ReduceAggregationFunction/createInputParameterMetadata
class ReduceAggregationFunction:    private static List<ParameterMetadata> createInputParameterMetadata(Type inputType, Type stateType)
    {
        return ImmutableList.of(
                new ParameterMetadata(STATE),
                new ParameterMetadata(INPUT_CHANNEL, inputType),
                new ParameterMetadata(INPUT_CHANNEL, stateType));
    }