Shared state

Hi!

I try add this to my class MyComponentState:
public List <VectorObject> vo = new ArrayList <VectorObject> ();

And acces from MyComponent :
Line line = new Line(0,0,400,400);
getState().vo.add(line);

I have a compile error :
[ERROR] property com.google.gwt.user.client.ui.UIObject Has the 'height' without getter defined.
[ERROR] Errors in 'com / Vaadin / customer / metadata / ConnectorBundleLoader.java
[ERROR] Line 76: Failed to resolve' com.vaadin.client.metadata.ConnectorBundleLoader 'via deferred binding

VectorObject comes package org.vaadin.gwtgraphics.client.VectorObject;

I look kind support here : https://vaadin.com/vaadin7
List, Map, Set

I do not understand what is happening.

Tanks for your help.