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