presto-ml/src/main/java/io/prestosql/plugin/ml/type/ModelType.java/ModelType/getObjectValue
class ModelType:    @Override
    public Object getObjectValue(ConnectorSession session, Block block, int position)
    {
        if (block.isNull(position)) {
            return null;
        }

        return format("<%s>", getTypeSignature()).getBytes(UTF_8);
    }