presto-main/src/main/java/io/prestosql/operator/aggregation/MapAggregationFunction.java/MapAggregationFunction/createInputParameterMetadata
class MapAggregationFunction:    private static List<ParameterMetadata> createInputParameterMetadata(Type keyType, Type valueType)
    {
        return ImmutableList.of(new ParameterMetadata(STATE),
                new ParameterMetadata(BLOCK_INPUT_CHANNEL, keyType),
                new ParameterMetadata(NULLABLE_BLOCK_INPUT_CHANNEL, valueType),
                new ParameterMetadata(BLOCK_INDEX));
    }