Aegis trying to instantiate abstract class

I have a big problem, look my example:

public abstract TemplateNode {}

public class FieldTemplate extends TemplateNode{};
public class FieldGroupTemplate extends TemplateNode{};

public class Template {
private List<TemplateNode> nodes;
..
}

Template t = new Template();
t.add(new FieldTemplate());
t.add(new FieldGroupTemplate());
// get service

service.insertTemplate( template );

****
I get error, 'cannot instantiate class null'.
In debug, i found this:
if(isInterface) {

} else if (isException) {

} else {
object = clazz.newInstance(); // but is abstract!!!
}
Xfire is trying to instantiate TemplateNode but he can't, because is abstract.
What i need to do?

Tkz.