ckeditor and NullPointerException

Hello,
I did the steps of this tutorial:
http://vaadin.com/learn (Vaadin application development - step-by-step).

I used vaadin 6.6.4 with ckeditor 1.4.1 (maven project), but when I turned this project in virgo, I had this exception:

HTTP Status 500 -

type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

javax.servlet.ServletException: java.lang.NullPointerException
com.vaadin.terminal.gwt.server.AbstractApplicationServlet.handleServiceException(AbstractApplicationServlet.java:999)
com.vaadin.terminal.gwt.server.AbstractApplicationServlet.service(AbstractApplicationServlet.java:548)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
root cause

java.lang.NullPointerException
java.util.Arrays$ArrayList.(Arrays.java:3357)
java.util.Arrays.asList(Arrays.java:3343)
com.vaadin.data.util.FilesystemContainer.addItemIds(FilesystemContainer.java:410)
com.vaadin.data.util.FilesystemContainer.getItemIds(FilesystemContainer.java:431)
com.vaadin.data.util.ContainerOrderedWrapper.updateOrderWrapper(ContainerOrderedWrapper.java:195)
com.vaadin.data.util.ContainerOrderedWrapper.(ContainerOrderedWrapper.java:101)
com.vaadin.ui.Table.setContainerDataSource(Table.java:1869)
com.vaadin.ui.Table.(Table.java:436)
com.mootwin.vaadin6.clean_vaadin2.DocumentmanagerApplication.(DocumentmanagerApplication.java:23)
sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
java.lang.reflect.Constructor.newInstance(Constructor.java:513)
java.lang.Class.newInstance0(Class.java:355)
java.lang.Class.newInstance(Class.java:308)
com.vaadin.terminal.gwt.server.ApplicationServlet.getNewApplication(ApplicationServlet.java:82)
com.vaadin.terminal.gwt.server.AbstractApplicationServlet.createApplication(AbstractApplicationServlet.java:973)
com.vaadin.terminal.gwt.server.AbstractApplicationServlet.findApplicationInstance(AbstractApplicationServlet.java:801)
com.vaadin.terminal.gwt.server.AbstractApplicationServlet.service(AbstractApplicationServlet.java:456)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
note The full stack trace of the root cause is available in the Apache Tomcat/6.0.29 logs.

thank you for helping me