File Upload Fails when no file selected

Hi,
Here is my code, which fires an Upload failed error, when I click on the Upload button without selecting any files. I know it is because of returning null value, but instead of this null I tried "return new ByteArrayOutputStream();" , still it shows Upload failed error.
I also tried to disable upload button using addChangeListener, but it disables the upload button only for first time.
How can I fix these issues, can anybody help me, Thanks in advance.!!!!!!!!!

private class ImageUploader implements Receiver, SucceededListener
    {
    private static final long serialVersionUID = -878399743277824104L;
    public File file;

    @Override
    public OutputStream receiveUpload(String filename, String mimeType)
    {
        FileOutputStream fos = null; // Stream to write to
        try
        {
        String tmpFolderLoc = getLocalFileLocation();
        // Open the file for writing.
        file = new File(tmpFolderLoc + File.separatorChar + filename);
        fos = new FileOutputStream(file);
    
        } catch (final java.io.FileNotFoundException e)
        {
        new Notification("Could not open file<br/>", e.getMessage(), Notification.Type.ERROR_MESSAGE).show(Page.getCurrent());
        return new ByteArrayOutputStream();
        }
        return fos; // Return the output stream to write to
    }

    @Override
    public void uploadSucceeded(SucceededEvent event)
    {
        attachCall.afterAttachementDone(file);
        // attachUpload.setButtonCaption(null);
        // refresh();
    }

    
    }

You should try new NullOutputStream() instead of ByteArrayOutputStream()
hope it works :)