NullPointerException for JFileChooser

Question

I've got problem with

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException

when you leave path empty I've got this message.

There are many topics here about it but I can't really figure it out. I've read the post about NullPointer.

As far as I understand it it's because one of my variable is empty, when the path not going to be selected. Thanks for help and sorry for to bother.

Error:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at com.bober.proj.WiewWindow$2.actionPerformed(WiewWindow.java:71)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$500(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)

WiewWindow.java

package com.bober.proj;

import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.DefaultComboBoxModel;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.filechooser.FileNameExtensionFilter;
import javax.swing.JFileChooser;

public class WiewWindow {

    protected static final JFileChooser String = null;
    private JFrame frame;

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    WiewWindow window = new WiewWindow();
                    window.frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the application.
     */
    public WiewWindow() {
        initialize();
    }

    /**
     * Initialize the contents of the frame.
     */
    private void initialize() {
        frame = new JFrame();
        frame.setBounds(100, 100, 450, 300);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().setLayout(null);
        JButton btnNewButton = new JButton("New button");
        JButton keyboardBT = new JButton("Keyboard...");

        final JComboBox<String> comboBox = new JComboBox<String>();
        final JComboBox<String> fixedFontSize = new JComboBox<String>();
        final JFileChooser chooser = new JFileChooser();

        comboBox.setModel(new DefaultComboBoxModel(new String[]{"Tak", "Nie", "Suka Bliac"}));
        fixedFontSize.setModel(new DefaultComboBoxModel(new String[]{"NO", "YES"}));

        btnNewButton.addActionListener(new ActionListener() {

            public void actionPerformed(ActionEvent arg0) {

                String text = (String) comboBox.getSelectedItem();
                String fixedF = (String) fixedFontSize.getSelectedItem();
                String path = chooser.getSelectedFile().getAbsolutePath();
                System.out.println(text);
                System.out.println(fixedF);
                System.out.println(path);

                FileOperation fo = new FileOperation();
                fo.writeToFle(text, fixedF, path);
            }
        });
        btnNewButton.setBounds(124, 206, 89, 23);
        frame.getContentPane().add(btnNewButton);

        comboBox.setBounds(246, 34, 121, 20);
        frame.getContentPane().add(comboBox);

        fixedFontSize.setBounds(10, 34, 89, 20);
        frame.getContentPane().add(fixedFontSize);

        keyboardBT.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                chooser.setCurrentDirectory(new java.io.File("C:\\test\\"));
                chooser.setDialogTitle("choosertitle");
                chooser.setFileSelectionMode(JFileChooser.FILES_AND_DIRECTORIES);
                chooser.setFileFilter(new FileNameExtensionFilter("KMP keyboard file", "kmp"));

                if (chooser.showOpenDialog(null) == JFileChooser.APPROVE_OPTION) {
                    System.out.println("getCurrentDirectory(): " + chooser.getCurrentDirectory());
                    System.out.println("getSelectedFile() : " + chooser.getSelectedFile().getName());

                } else {
                    System.out.println("No Selection");
                }

            }
        });
        keyboardBT.setBounds(246, 206, 105, 23);
        frame.getContentPane().add(keyboardBT);

    }
}

FileOperation.java

package com.bober.proj;

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;

import javax.swing.JFileChooser;

public class FileOperation {

    public void writeToFle(String text, String fixedF, String path) {
        try {
            File dir = new File("C:\\test");
            File[] directoryListing = dir.listFiles();
            if (directoryListing != null) {
                for (File child : directoryListing) {
                    FileWriter writer = new FileWriter(child, true);
                    PrintWriter out = new PrintWriter(writer);
                    if (text == "Tak") {

                    } else {
                        out.println(text);
                    }
                    if (fixedF == "NO") {

                    } else {
                        out.println("fixedFontSize=true");
                    }
                    if (path != "") {
                        out.println("Filename=" + path);
                    } else {
                        System.out.println("Could not load path");
                    }
                    out.close();
                }
            }
        } catch (IOException e) {
            System.out.println("File error " + e.getMessage());
        }
        System.out.println("File saved");
    }
}