i try to use the mediaoutput sample but can't get it work. mediadata is always null

my page is

<?xml version="1.0" encoding="ISO-8859-1"?>
<ui:composition xmlns="http://www.w3.org/1999/xhtml"
 xmlns:ui="http://java.sun.com/jsf/facelets"
 xmlns:h="http://java.sun.com/jsf/html"
 xmlns:f="http://java.sun.com/jsf/core"
 xmlns:rich="http://richfaces.org/rich"
 xmlns:a4j="http://richfaces.org/a4j"
 xmlns:s="http://jboss.com/products/seam/taglib">
<h:panelGrid columns="2" >
<h:panelGroup id="thumbs">
</h:panelGroup>
 <a4j:mediaOutput element="img" cacheable="false" session="false"
 createContent="#{PDFImaging.paintpage}" value="#{mediaData}" mimeType="image/png" />

</h:panelGrid>
</ui:composition>

public class MediaData implements Serializable{

 private static final long serialVersionUID = 1L;
 Integer Width=50;
 Integer Height=110;
 Color Background=new Color(0,0,0);
 Color DrawColor=new Color(255,255,255);
 public MediaData() {
 }
 public Color getBackground() {
 return Background;
 }
 public void setBackground(Color background) {
 Background = background;
 }
 public Color getDrawColor() {
 return DrawColor;
 }
 public void setDrawColor(Color drawColor) {
 DrawColor = drawColor;
 }
 public Integer getHeight() {
 return Height;
 }
 public void setHeight(Integer height) {
 Height = height;
 }
 public Integer getWidth() {
 return Width;
 }
 public void setWidth(Integer width) {
 Width = width;
 }
}



@Name("PDFImaging")
@Scope(ScopeType.PAGE)
public class PDFImaging {


 String pdfsource;
 String currentimage;
 ArrayList<MediaBean> thumbs = new ArrayList<MediaBean>();

 boolean lbinit =false;

 public void init() {
 int count=0;
 File dir= new File("D:/seampages");
 for(File f : dir.listFiles()) {
 if (f.isDirectory() == false) {
 MediaBean mb = new MediaBean();
 mb.setImagefile(f.getAbsolutePath());
 System.out.println("Adding " + f.getAbsolutePath());
 thumbs.add(mb );
 count++;
 }
 if ( count > 20 ) break;
 }
 lbinit = true;
 }

 public void paintpage(OutputStream out, Object data) throws IOException{
 System.out.println("Paint page " );
 if ( data != null) System.out.println(data.getClass().getName());
 else System.out.println("is null!!!!");
 try {
 if (data instanceof MediaData) {

 MediaData paintData = (MediaData) data;
 BufferedImage img = new BufferedImage(paintData.getWidth(),paintData.getHeight(),BufferedImage.TYPE_INT_RGB);
 img = ImageIO.read(new File("D:/seampages/1.png"));


 ImageIO.write(img,"jpeg",out);

 }
 } catch (Exception e) {
 // TODO Auto-generated catch block
 e.printStackTrace();
 }
 }

 public String getPdfsource() {
 return pdfsource;
 }
 public void setPdfsource(String pdfsource) {
 this.pdfsource = pdfsource;
 }
 public String getCurrentimage() {
 return currentimage;
 }
 public void setCurrentimage(String currentimage) {
 this.currentimage = currentimage;
 }
 public ArrayList<MediaBean> getThumbs() {
 if ( lbinit == false ) init();
 return thumbs;
 }
 public void setThumbs(ArrayList<MediaBean> thumbs) {
 this.thumbs = thumbs;
 }


}