Modifying XML file structure (Java)

import java.io.FileWriter;
import java.io.File;
import java.io.IOException;
 
import org.dom4j.io.*;
import org.dom4j.*;
 
 
public class MyClass {
 
    public static void main(String[] args) {
 
        File dir = new File("in/emissions");
        File[] files = dir.listFiles();
        for (int i=0; i<files.length; i++) {
            if (!files[i].getName().endsWith(".xml")) {
                continue;
            }
 
            XMLWriter output = null;
            try {
                Element emission = new SAXReader().read(files[i]).getRootElement();
 
                Element sondage = emission.addElement("pr:sondage");
                sondage.addAttribute("xsi:nil", "true");
                sondage.setText("n/a");
 
                FileWriter writer = new FileWriter("out/" + files[i].getName());
                output = new XMLWriter(writer, OutputFormat.createPrettyPrint());
 
                output.write(emission);		
            } catch (IOException e) {
                e.printStackTrace();
            } catch (DocumentException e)
                e.printStackTrace();
            } finally {
                try {
                    output.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}