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:
com.zamek.pollack.quiz.QuizWidgetset in file:/home/zamek/workspace/Quiz/target/classes

auto discovered modules [com.zamek.pollack.quiz.QuizWidgetset]

Compiling module com.zamek.pollack.quiz.QuizWidgetset
Tracing compile failure path for type ‘’
Errors in ‘jar:file:/home/zamek/.m2/repository/com/vaadin/vaadin-client/7.5.6/vaadin-client-7.5.6.jar!/com/goog

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"?>

Do I need to compile the widgetset? How can I set validation-api in gwt.xml, if yes.