ViewExpiredException, когда я использую @ViewScoped

У меня проблема с моим h: commandButton «Вход»: когда я использую @ViewScoped и нажимаю эту кнопку, возникает ViewExpiredException, но когда я использую @SessionScoped, ошибки нет.

Трассировки стека:

javax.faces.application.ViewExpiredException: /pages/register.xhtmlNo saved view state could be found for the view identifier: /pages/register.xhtml
at org.apache.myfaces.lifecycle.RestoreViewExecutor.execute(RestoreViewExecutor.java:132)
at org.apache.myfaces.lifecycle.LifecycleImpl.executePhase(LifecycleImpl.java:170)
at org.apache.myfaces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:117)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:197)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.primefaces.webapp.filter.FileUploadFilter.doFilter(FileUploadFilter.java:79)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.tomee.catalina.OpenEJBValve.invoke(OpenEJBValve.java:45)
at org.apache.tomee.catalina.OpenEJBValve.invoke(OpenEJBValve.java:45)
at org.apache.tomee.catalina.OpenEJBValve.invoke(OpenEJBValve.java:45)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:936)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:724)

моя страница:

            <h:form>
                <h:panelGrid columns="2" >
                    <h:outputLabel value="Login:"/>
                    <h:inputText value="#{registerController.registerLog}"/>
                    <h:outputLabel value="#{msg.password}"/>
                    <h:inputSecret id="pass" value=""/>

                    <h:column/>
                    <h:commandButton value="Login" action="#{registerController.login}"/> 

                </h:panelGrid> 
            </h:form>

и это мой класс RegisterController:

@ManagedBean
@ViewScoped
public class RegisterController {

private String registerLog = "";
private String registerPass = "";


/**
 * Creates a new instance of RegisterController
 */
public RegisterController() {
}

//getters, setters

public String login(){

    return null;

}