cannot compile project with maven

Hi All,

I made a simple Vaadin project V7.5.6 with maven. Everything is working well with mvn jetty:run, but when I want to make a war with mvn clean vaadin:compile-theme package I get an error:
 Widgetsets found from classpath:
[INFO]  com.zamek.pollack.quiz.QuizWidgetset in file:/home/zamek/workspace/Quiz/target/classes
...
 auto discovered modules [com.zamek.pollack.quiz.QuizWidgetset]
[INFO] Compiling module com.zamek.pollack.quiz.QuizWidgetset
[INFO]    Tracing compile failure path for type 'com.google.gwt.validation.client.constraints.SizeValidatorForArrayOfChar'
[INFO]       [ERROR] Errors in 'jar:file:/home/zamek/.m2/repository/com/vaadin/vaadin-client/7.5.6/vaadin-client-7.5.6.jar!/com/goog
le/gwt/validation/client/constraints/SizeValidatorForArrayOfChar.java'

I need to use validation-api in my project, but I don't need widgetset. That is my QuizWidgetset.gwt.xml: 
<?xml version="1.0" encoding="UTF-8"?>                                                                                               
<!DOCTYPE module PUBLIC "-//Google Inc.//DTD Google Web Toolkit 2.5.1//EN"                                                           
       "http://google-web-toolkit.googlecode.com/svn/tags/2.5.1/distro-source/core/src/gwt-module.dtd">                             
<module>                                                                                                                             
   <inherits name="com.vaadin.DefaultWidgetSet"/>                                                                                   
</module>                                                                                                                            
             
Do I need to compile the widgetset? How can I set validation-api in gwt.xml, if yes. 

thx
Zamek