Error creating bean with name 'springSecurityFilterChain'

I have been following the Spring Security Reference and i added only this classes:

@Configuration
@EnableWebMvcSecurity
public class WebSecurityConfig extends WebSecurityConfigurerAdapter {

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
        .authorizeRequests()
            .anyRequest().authenticated()
            .and()
        .formLogin().loginPage("/login")
        .permitAll()
            .and()
        .logout()
        .permitAll();
    }

    @Autowired
    public void configureGlobal(AuthenticationManagerBuilder auth) throws Exception {
        auth
            .inMemoryAuthentication()
                .withUser("user").password("password").roles("USER").and()
                .withUser("user").password("password").roles("USER", "ADMIN");
    }
}

and

public class SecurityInitializer extends AbstractSecurityWebApplicationInitializer {


}

but when i run the server, an exception is thrown, i don't know what i am doing wrong, can you help me please?

This is the stacktrace:

javax.servlet.UnavailableException: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'springSecurityFilterChain' defined in class path resource [org/springframework/security/config/annotation/web/configuration/WebSecurityConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [javax.servlet.Filter]: Factory method 'springSecurityFilterChain' threw exception; nested exception is java.lang.IllegalArgumentException: [Assertion failed] - this expression must be true
at org.mortbay.jetty.servlet.ServletHolder.makeUnavailable(ServletHolder.java:415)
at org.mortbay.jetty.servlet.ServletHolder.initServlet(ServletHolder.java:458)
at org.mortbay.jetty.servlet.ServletHolder.doStart(ServletHolder.java:263)
at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
at org.mortbay.jetty.servlet.ServletHandler.initialize(ServletHandler.java:685)
at org.mortbay.jetty.servlet.Context.startContext(Context.java:140)
at org.mortbay.jetty.webapp.WebAppContext.startContext(WebAppContext.java:1272)
at org.mortbay.jetty.handler.ContextHandler.doStart(ContextHandler.java:517)
at org.mortbay.jetty.webapp.WebAppContext.doStart(WebAppContext.java:489)
at org.gradle.api.plugins.jetty.internal.JettyPluginWebAppContext.doStart(JettyPluginWebAppContext.java:112)
at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
at org.mortbay.jetty.handler.HandlerCollection.doStart(HandlerCollection.java:152)
at org.mortbay.jetty.handler.ContextHandlerCollection.doStart(ContextHandlerCollection.java:156)
at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
at org.mortbay.jetty.handler.HandlerCollection.doStart(HandlerCollection.java:152)
at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
at org.mortbay.jetty.handler.HandlerWrapper.doStart(HandlerWrapper.java:130)
at org.mortbay.jetty.Server.doStart(Server.java:224)
at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
at org.gradle.api.plugins.jetty.internal.Jetty6PluginServer.start(Jetty6PluginServer.java:111)
at org.gradle.api.plugins.jetty.AbstractJettyRunTask.startJettyInternal(AbstractJettyRunTask.java:238)
at org.gradle.api.plugins.jetty.AbstractJettyRunTask.startJetty(AbstractJettyRunTask.java:191)
at org.gradle.api.plugins.jetty.AbstractJettyRunTask.start(AbstractJettyRunTask.java:162)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
....