presto-main/src/main/java/io/prestosql/operator/MergeOperator.java/MergeOperator/close
class MergeOperator:    @Override
    public void close()
    {
        try {
            closer.close();
            closed = true;
        }
        catch (IOException e) {
            throw new UncheckedIOException(e);
        }
    }