Android中的SimpleXML反序列化错误

@Root
public class A {
    @ElementList
    private ArrayList<B> b;

    getters, setters...
}  


public class B{
    @Element(name="C", required=false)
    private C c;

    getters, setters...
}  

public class C{
    private int id;
    private String name;

    getters, setters...
}  

<A>
   <B>
       <C i:nil="true" />
   </B>
</A>