Help!,the property 'var' of tree doesn't play role

[bradford]

The following is my tree:

<rich:tree style="width:300px" switchType="client"
 value="#{simpleTreeBean.treeNode}" var="item" nodeFace="#{item.type}">

 <rich:treeNode type="common">
 <h:selectBooleanCheckbox value="#{item.selected}"/>
 <h:outputText value="#{item.title}" />
 </rich:treeNode>
</rich:tree>

SimpleTreeBean

public class SimpleTreeBean {

 private CommonNode rootNode = null;

 //init tree;
 private CommonNode getTreeByStr(List list,CommonNode rootNode,String index){
 int count = 0;
 for(int i=0;i<list.size();i++){
 String str = (String)list.get(i);
 StringTokenizer toc = new StringTokenizer(str,",");

 String t1 = toc.nextToken();
 String t2 = toc.nextToken();
 String t3 = toc.nextToken();
 if(t1.equals(index)){
 CommonNode nodeImpl = new CommonNode();
 nodeImpl.setTitle(t3);
 rootNode.addChild(new Integer(count), nodeImpl);
 getTreeByStr(list,nodeImpl,t2);
 count++;
 }


 }

 return rootNode;

 }
 //init tree;
 private void loadTree(){

 rootNode = new CommonNode();
 String t1 = "0,1,a";
 String t11 = "1,2,a1";
 String t12 = "1,3,a2";
 String t111 = "2,7,a11";
 String t112 = "2,8,a12";
 String t2 = "0,4,b";
 String t21 = "4,5,b1";
 String t22 = "4,6,b2";
 List list = new ArrayList();
 list.add(t1);
 list.add(t11);
 list.add(t12);
 list.add(t2);
 list.add(t21);
 list.add(t111);
 list.add(t112);
 rootNode = getTreeByStr(list,rootNode,"0");


 }
 public TreeNode getTreeNode() {

 loadTree();

 return rootNode;
 }

}

CommonNode

public class CommonNode implements TreeNode {

 private static final long serialVersionUID = -5498990493803705085L;
 private Object data;
 private TreeNode parent;
 private boolean selected;
 private Object realData;
 private String title;
 private Object state1;
 private Object state2;

 private Map childrenMap = new LinkedHashMap();

 public Object getData() {
 return data;
 }

 public TreeNode getChild(Object identifier) {
 return (TreeNode) childrenMap.get(identifier);
 }

 public void addChild(Object identifier, TreeNode child) {
 child.setParent(this);
 childrenMap.put(identifier, child);
 }

 public void removeChild(Object identifier) {
 TreeNode treeNode = (TreeNode) childrenMap.remove(identifier);
 if (treeNode != null) {
 treeNode.setParent(null);
 }
 }

 public void setData(Object data) {
 this.data = data;
 }

 public TreeNode getParent() {
 return parent;
 }

 public void setParent(TreeNode parent) {
 this.parent = parent;
 }

 public Iterator getChildren() {
 return childrenMap.entrySet().iterator();
 }

 public boolean isLeaf() {
 return childrenMap.isEmpty();
 }

 public boolean isSelected() {
 return selected;
 }

 public void setSelected(boolean selected) {
 this.selected = selected;
 }

 public Object getRealData() {
 return realData;
 }

 public void setRealData(Object realData) {
 this.realData = realData;
 }
 public String getType() {
 return "common";
 }

 public String getTitle() {
 return title;
 }

 public void setTitle(String title) {
 this.title = title;
 }

 public Object getState1() {
 return state1;
 }

 public void setState1(Object state1) {
 this.state1 = state1;
 }

 public Object getState2() {
 return state2;
 }

 public void setState2(Object state2) {
 this.state2 = state2;
 }
}

when i wanna load my tree,An Error Occurred:
/platform/log/tree.xhtml @19,87 nodeFace="#{item.type}": Bean: java.lang.String, property: type
Please help me,thanks ~~~