presto-main/src/main/java/io/prestosql/operator/aggregation/multimapagg/MultimapAggregationFunction.java/MultimapAggregationFunction/createInputParameterMetadata
class MultimapAggregationFunction:    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));
    }