Suddenly getting: java.lang.IllegalArgumentException: image == null

Question

Ive been able to save an output image fine using the same code as I'm using now, however, as I've been updating my application it appears that the code to save my image has now broke in some way.

If I put it so that the file saves after 'combining' to create the output it works fine, and I have resorted to using this to ensure the application is actually working properly (which it is). I did want the user of the application to be able to control the filenames so that nothing is overwritten and as I say, it worked fine previously.

The code I'm using to save the image is here:

private void saveButtonActionPerformed(java.awt.event.ActionEvent evt) {                                           
        // TODO add your handling code here:
        String fileName = JOptionPane.showInputDialog(null, "Save as...","");
        save(fileName, combinedImage);
    } 

---

public static void save(String fileName, BufferedImage combinedImage) {
            try {
            File outputfile = new File(fileName+".png");
            ImageIO.write(combinedImage, "png", outputfile);
            JOptionPane.showMessageDialog(null, "File successfully saved as: "+outputfile);
            System.out.println("File saved successfully: "+outputfile);
            }
            catch(IOException e) {
            JOptionPane.showMessageDialog(null,"Save Image Error", "Save Image Error", WARNING_MESSAGE);
            }
    }

Where combinedImage is the output I wish to save as a PNG image.

---

The full error message is also here:

Exception in thread "AWT-EventQueue-0" java.lang.IllegalArgumentException: image == null!
    at javax.imageio.ImageTypeSpecifier.createFromRenderedImage(ImageTypeSpecifier.java:925)
    at javax.imageio.ImageIO.getWriter(ImageIO.java:1591)
    at javax.imageio.ImageIO.write(ImageIO.java:1520)
    at grey2RGB.save(grey2RGB.java:808)
    at grey2RGB.saveButtonActionPerformed(grey2RGB.java:721)
    at grey2RGB.access$2100(grey2RGB.java:29)
    at grey2RGB$22.actionPerformed(grey2RGB.java:440)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
    at java.awt.Component.processMouseEvent(Component.java:6505)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
    at java.awt.Component.processEvent(Component.java:6270)
    at java.awt.Container.processEvent(Container.java:2229)
    at java.awt.Component.dispatchEventImpl(Component.java:4861)
    at java.awt.Container.dispatchEventImpl(Container.java:2287)
    at java.awt.Component.dispatchEvent(Component.java:4687)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
    at java.awt.Container.dispatchEventImpl(Container.java:2273)
    at java.awt.Window.dispatchEventImpl(Window.java:2719)
    at java.awt.Component.dispatchEvent(Component.java:4687)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:729)
    at java.awt.EventQueue.access$200(EventQueue.java:103)
    at java.awt.EventQueue$3.run(EventQueue.java:688)
    at java.awt.EventQueue$3.run(EventQueue.java:686)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
    at java.awt.EventQueue$4.run(EventQueue.java:702)
    at java.awt.EventQueue$4.run(EventQueue.java:700)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:699)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

Line 808 is

ImageIO.write(combinedImage, "png", outputfile);

Line 721 is

save(fileName, combinedImage);

Any help would be appreciated!

Answer 1

Often this sort of problem is caused by there being more than one variable named combinedImage (and using the wrong one). For example, check:

• that you do not have multiple variables called combinedImage in different places
• that if combinedImage is a member variable, that you are using it from the same instance of object wherever you expect to do so

If that doesn't help, then get out your debugger and trace the code.