Erreur Java : Je n'arrive pas à retirer mon erreur

package image;

import java.awt.EventQueue;
import java.awt.Toolkit;
import java.awt.Color;
import java.awt.BorderLayout;
import java.awt.Font;
import java.awt.Window.Type;

import javax.swing.filechooser.FileNameExtensionFilter;
import javax.swing.filechooser.FileSystemView;

import com.opencsv.exceptions.CsvException;

//import image.conversion.XMLCreators;

import java.awt.Button;
import java.awt.event.ActionListener;
import java.io.File;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.awt.event.ActionEvent;
import java.awt.event.*;
import java.awt.*;
import javax.swing.*;

public class fenetre extends conversion {
 //char t = ',';
 private JFrame frmFaiaPourFidexpert;
 
 public static void main(String[] args) {
  EventQueue.invokeLater(new Runnable(){
   public void run(){
    try {
     fenetre window = new fenetre();
     window.frmFaiaPourFidexpert.setVisible(true);
    } catch (Exception e) {
     e.printStackTrace();
    }
   }
  });
 }

 public fenetre(){
  initialize();
 }

 /**
* Initialize the contents of the frame.
*/
 private void initialize(){
  frmFaiaPourFidexpert = new JFrame();
  frmFaiaPourFidexpert.setBackground(new Color(245, 222, 179));
  frmFaiaPourFidexpert.setTitle("FAIA pour FID-Expert");
  frmFaiaPourFidexpert.setForeground(Color.BLACK);
  frmFaiaPourFidexpert.setIconImage(Toolkit.getDefaultToolkit().getImage(fenetre.class.getResource("/image/lux.png")));
  frmFaiaPourFidexpert.setBounds(100, 100, 470, 440);
  frmFaiaPourFidexpert.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  frmFaiaPourFidexpert.setResizable(false);
  
  JButton btnNewButton = new JButton("Convertir un fichier");
  btnNewButton.setBounds(0, 302, 456, 29);
  btnNewButton.addActionListener(new ActionListener(){
   public void actionPerformed(ActionEvent e) {
    String s = e.getActionCommand();
       
       if (s.equals("Convertir un fichier")) {
        JFileChooser fichier = new JFileChooser( FileSystemView.getFileSystemView().getHomeDirectory());
        fichier.setDialogTitle("Choississez votre fichier .csv");
        fichier.setAcceptAllFileFilterUsed(false);
        FileNameExtensionFilter filter = new FileNameExtensionFilter("Fichier .csv","csv");
        fichier.addChoosableFileFilter(filter);
        int res = fichier.showOpenDialog(null);
           // Enregistrez le fichier
           if (res == JFileChooser.APPROVE_OPTION) {
             String XML;
             XML = null;
             
             //File file = fichier.getSelectedFile();
             String fi = fichier.getName();
             XMLCreators xmlCreators = new XMLCreators();
       xmlCreators.convertFile(fi, XML, '\t');
             //conversion.XMLCreators.convertFile(String,String,char);
            
             
             
          }
        ;
         
       }
   }
  });
  frmFaiaPourFidexpert.getContentPane().setLayout(null);
  btnNewButton.setForeground(Color.BLACK);
  btnNewButton.setFont(new Font("Yu Gothic UI", Font.BOLD, 14));
  btnNewButton.setBackground(new Color(168, 146, 28));
  frmFaiaPourFidexpert.getContentPane().add(btnNewButton);
  
  JLabel lblNewLabel = new JLabel("");
  lblNewLabel.setBounds(0, 14, 456, 328);
  lblNewLabel.setHorizontalAlignment(SwingConstants.CENTER);
  lblNewLabel.setIcon(new ImageIcon(fenetre.class.getResource("/image/fid.png")));
  frmFaiaPourFidexpert.getContentPane().add(lblNewLabel);
  
  JLabel lblNewLabel_1 = new JLabel("                Conversion fichier pour FAIA");
  lblNewLabel_1.setBounds(0, 0, 456, 24);
  lblNewLabel_1.setBackground(new Color(218, 165, 32));
  lblNewLabel_1.setFont(new Font("Microsoft New Tai Lue", Font.BOLD, 18));
  frmFaiaPourFidexpert.getContentPane().add(lblNewLabel_1);
  
  JMenuBar menuBar = new JMenuBar();
  frmFaiaPourFidexpert.setJMenuBar(menuBar);
  
  JMenu mnNewMenu = new JMenu("Aide");
  JMenuItem menuItem = new JMenuItem("?");
  menuItem.addActionListener(new ActionListener(){
   public void actionPerformed(ActionEvent e) {
    String w = e.getActionCommand();
    JFrame frame = new JFrame();
    if (w.equals("?")) {
     JDialog d = new JDialog(frame, "Aide");
     JLabel l = new JLabel("Le bouton convertit un fichier .csv en .xml directement sur votre PC");
     d.getContentPane().add(l);
     d.setIconImage(Toolkit.getDefaultToolkit().getImage(fenetre.class.getResource("/image/lux.png")));
     d.setSize(400,100);
     d.setVisible(true);
    }
   }
  });
  mnNewMenu.add(menuItem);
  menuBar.add(mnNewMenu);
 }

}

package image;
import com.opencsv.CSVParser;
import com.opencsv.CSVParserBuilder;
import com.opencsv.CSVReader;
import com.opencsv.CSVReaderBuilder;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.FactoryConfigurationError;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Result;
import javax.xml.transform.Source;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import org.w3c.dom.Document;
import org.w3c.dom.Element;

public class conversion {
    public static void main(String[] args) {
        new conversion();
    }

   // public conversion(){
    //    new XMLCreators().convertFile("Test.csv", "Test.xml", '\t');
    //}

    public class XMLCreators {
        // Protected Properties

        protected DocumentBuilderFactory domFactory = null;
        protected DocumentBuilder domBuilder = null;

        public XMLCreators(){
            try {
                domFactory = DocumentBuilderFactory.newInstance();
                domBuilder = domFactory.newDocumentBuilder();
            } catch (FactoryConfigurationError exp) {
                System.err.println(exp.toString());
            } catch (ParserConfigurationException exp) {
                System.err.println(exp.toString());
            } catch (Exception exp) {
                System.err.println(exp.toString());
            }
        }

        public int convertFile(String csvFileName, String xmlFileName, char delimiter) {

            int rowsCount = -1;
            BufferedReader csvReader;
            try {
                Document newDoc = domBuilder.newDocument();
                // Root element
                Element rootElement = newDoc.createElement("XMLCreators");
                newDoc.appendChild(rootElement);
                // Read csv file
                csvReader = new BufferedReader(new FileReader(csvFileName));

                //** Now using the OpenCSV **//
                CSVParser parser = new CSVParserBuilder()
                        .withSeparator(delimiter)
                        .build();

                CSVReader reader = new CSVReaderBuilder(new FileReader(csvFileName))
                        .withCSVParser(parser)
                        .build();
                //CSVReader reader = new CSVReader(csvReader);
                String[] nextLine;
                int line = 0;
                List<String> headers = new ArrayList<String>(5);
                while ((nextLine = reader.readNext()) != null) {
                    if (line == 0) { // Header row
                        for (String col : nextLine) {
                            headers.add(col);
                        }
                    } else { // Data row
                        Element rowElement = newDoc.createElement("row");
                        rootElement.appendChild(rowElement);

                        int col = 0;
                        for (String value : nextLine) {
                            String header = headers.get(col).replaceAll("[\\t\\p{Zs}\\u0020]", "_");

                            Element curElement = newDoc.createElement(header);
                            curElement.appendChild(newDoc.createTextNode(value.trim()));
                            rowElement.appendChild(curElement);

                            col++;
                        }
                    }
                    line++;
                }
                //** End of CSV parsing**//

                FileWriter writer = null;

                try {

                    writer = new FileWriter(new File(xmlFileName));

                    TransformerFactory tranFactory = TransformerFactory.newInstance();
                    Transformer aTransformer = tranFactory.newTransformer();
                    aTransformer.setOutputProperty(OutputKeys.INDENT, "yes");
                    aTransformer.setOutputProperty(OutputKeys.METHOD, "xml");
                    aTransformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "4");

                    Source src = new DOMSource(newDoc);
                    Result result = new StreamResult(writer);
                    aTransformer.transform(src, result);

                    writer.flush();

                } catch (Exception exp) {
                    exp.printStackTrace();
                } finally {
                    try {
                        writer.close();
                    } catch (Exception e) {
                    }
                }

                // Output to console for testing
                // Resultt result = new StreamResult(System.out);
            } catch (IOException exp) {
                exp.printStackTrace();
            } catch (Exception exp) {
                exp.printStackTrace();
            }
            return rowsCount;
            // "XLM Document has been created" + rowsCount;
        }
    }
}