Wicket 1.4 apps with file upload in form don't work. Stack trace:

07:58:44,543 ERROR [org.apache.wicket.RequestCycle] (default task-34) UT000017: Form value is a file, use getFile() instead: java.lang.IllegalStateException: UT000017: Form value is a file, use getFile() instead
at io.undertow.server.handlers.form.FormData$FormValueImpl.getValue(FormData.java:206) [undertow-core-1.0.0.Alpha21.jar:1.0.0.Alpha21]
at io.undertow.servlet.spec.HttpServletRequestImpl.getParameterMap(HttpServletRequestImpl.java:659) [undertow-servlet-1.0.0.Alpha21.jar:1.0.0.Alpha21]
at org.apache.wicket.protocol.http.servlet.ServletWebRequest.getParameterMap(ServletWebRequest.java:148) [wicket-1.4.15.jar:1.4.15]
at org.apache.wicket.protocol.http.request.WebRequestCodingStrategy.decode(WebRequestCodingStrategy.java:218) [wicket-1.4.15.jar:1.4.15]
at org.apache.wicket.Request.getRequestParameters(Request.java:183) [wicket-1.4.15.jar:1.4.15]
at org.apache.wicket.RequestCycle.step(RequestCycle.java:1310) [wicket-1.4.15.jar:1.4.15]
at org.apache.wicket.RequestCycle.steps(RequestCycle.java:1436) [wicket-1.4.15.jar:1.4.15]
at org.apache.wicket.RequestCycle.request(RequestCycle.java:545) [wicket-1.4.15.jar:1.4.15]
at org.apache.wicket.protocol.http.WicketFilter.doGet(WicketFilter.java:486) [wicket-1.4.15.jar:1.4.15]
at org.apache.wicket.protocol.http.WicketFilter.doFilter(WicketFilter.java:319) [wicket-1.4.15.jar:1.4.15]
at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:56) [undertow-servlet-1.0.0.Alpha21.jar:1.0.0.Alpha21]
at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:132) [undertow-servlet-1.0.0.Alpha21.jar:1.0.0.Alpha21]
at io.undertow.servlet.handlers.FilterHandler.handleRequest(FilterHandler.java:85) [undertow-servlet-1.0.0.Alpha21.jar:1.0.0.Alpha21]
at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:56) [undertow-servlet-1.0.0.Alpha21.jar:1.0.0.Alpha21]
at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36) [undertow-servlet-1.0.0.Alpha21.jar:1.0.0.Alpha21]
at org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:78)
at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:115) [undertow-servlet-1.0.0.Alpha21.jar:1.0.0.Alpha21]
at io.undertow.security.handlers.AuthenticationCallHandler.handleRequest(AuthenticationCallHandler.java:52) [undertow-core-1.0.0.Alpha21.jar:1.0.0.Alpha21]
at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:45) [undertow-core-1.0.0.Alpha21.jar:1.0.0.Alpha21]
at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:65) [undertow-servlet-1.0.0.Alpha21.jar:1.0.0.Alpha21]
at io.undertow.security.handlers.SecurityInitialHandler.handleRequest(SecurityInitialHandler.java:70) [undertow-core-1.0.0.Alpha21.jar:1.0.0.Alpha21]
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:25) [undertow-core-1.0.0.Alpha21.jar:1.0.0.Alpha21]
at org.wildfly.extension.undertow.security.SecurityContextCreationHandler.handleRequest(SecurityContextCreationHandler.java:54)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:25) [undertow-core-1.0.0.Alpha21.jar:1.0.0.Alpha21]
at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:127) [undertow-servlet-1.0.0.Alpha21.jar:1.0.0.Alpha21]
at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:114) [undertow-servlet-1.0.0.Alpha21.jar:1.0.0.Alpha21]
at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:47) [undertow-servlet-1.0.0.Alpha21.jar:1.0.0.Alpha21]
at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:90) [undertow-servlet-1.0.0.Alpha21.jar:1.0.0.Alpha21]
at io.undertow.server.HttpHandlers.executeRootHandler(HttpHandlers.java:36) [undertow-core-1.0.0.Alpha21.jar:1.0.0.Alpha21]
at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:607) [undertow-core-1.0.0.Alpha21.jar:1.0.0.Alpha21]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) [rt.jar:1.7.0_21]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) [rt.jar:1.7.0_21]
at java.lang.Thread.run(Thread.java:722) [rt.jar:1.7.0_21]