NPE while trying to reorder folder

org.apache.wicket.WicketRuntimeException: Error attaching this container for rendering: [MarkupContainer [Component id = body]]
at org.apache.wicket.MarkupContainer.onBeforeRenderChildren(MarkupContainer.java:1739)
at org.apache.wicket.Component.onBeforeRender(Component.java:3855)
at org.apache.wicket.Component.internalBeforeRender(Component.java:1061)
at org.apache.wicket.Component.beforeRender(Component.java:1095)
at org.apache.wicket.MarkupContainer.onBeforeRenderChildren(MarkupContainer.java:1727)
at org.apache.wicket.Component.onBeforeRender(Component.java:3855)
at org.apache.wicket.Component.internalBeforeRender(Component.java:1061)
at org.apache.wicket.Component.beforeRender(Component.java:1095)
at org.apache.wicket.MarkupContainer.onBeforeRenderChildren(MarkupContainer.java:1727)
at org.apache.wicket.Component.onBeforeRender(Component.java:3855)
at org.apache.wicket.Component.internalBeforeRender(Component.java:1061)
at org.apache.wicket.Component.beforeRender(Component.java:1095)
at org.apache.wicket.MarkupContainer.onBeforeRenderChildren(MarkupContainer.java:1727)
at org.apache.wicket.Component.onBeforeRender(Component.java:3855)
at org.apache.wicket.Component.internalBeforeRender(Component.java:1061)
at org.apache.wicket.Component.beforeRender(Component.java:1095)
at org.apache.wicket.MarkupContainer.onBeforeRenderChildren(MarkupContainer.java:1727)
at org.apache.wicket.Component.onBeforeRender(Component.java:3855)
at org.apache.wicket.Component.internalBeforeRender(Component.java:1061)
at org.apache.wicket.Component.beforeRender(Component.java:1095)
at org.apache.wicket.MarkupContainer.onBeforeRenderChildren(MarkupContainer.java:1727)
at org.apache.wicket.Component.onBeforeRender(Component.java:3855)
at org.hippoecm.frontend.dialog.ModalWindow.onBeforeRender(ModalWindow.java:765)
at org.apache.wicket.Component.internalBeforeRender(Component.java:1061)
at org.apache.wicket.Component.beforeRender(Component.java:1095)
at org.apache.wicket.Component.prepareForRender(Component.java:2225)
at org.apache.wicket.Component.prepareForRender(Component.java:2262)
at org.apache.wicket.ajax.AjaxRequestTarget.respondComponent(AjaxRequestTarget.java:805)
at org.apache.wicket.ajax.AjaxRequestTarget.respondComponents(AjaxRequestTarget.java:681)
at org.apache.wicket.ajax.AjaxRequestTarget.respond(AjaxRequestTarget.java:591)
at org.apache.wicket.request.AbstractRequestCycleProcessor.respond(AbstractRequestCycleProcessor.java:105)
at org.apache.wicket.RequestCycle.processEventsAndRespond(RequestCycle.java:1258)
at org.apache.wicket.RequestCycle.step(RequestCycle.java:1329)
at org.apache.wicket.RequestCycle.steps(RequestCycle.java:1428)
at org.apache.wicket.RequestCycle.request(RequestCycle.java:545)
at org.apache.wicket.protocol.http.WicketFilter.doGet(WicketFilter.java:479)
at org.apache.wicket.protocol.http.WicketFilter.doFilter(WicketFilter.java:312)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at org.hippoecm.frontend.ResourceRewriteFilter.doFilter(ResourceRewriteFilter.java:127)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at org.hippoecm.frontend.plugins.login.ConcurrentLoginFilter.doFilter(ConcurrentLoginFilter.java:54)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
at org.mortbay.jetty.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:230)
at org.mortbay.jetty.handler.HandlerCollection.handle(HandlerCollection.java:114)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.Server.handle(Server.java:326)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:923)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:547)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:212)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409)
at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)
Caused by: java.lang.NullPointerException
at org.hippoecm.frontend.plugins.standards.list.ListCell.<init>(ListCell.java:88)
at org.hippoecm.frontend.plugins.standards.list.ListColumn.populateItem(ListColumn.java:124)
at org.apache.wicket.extensions.markup.html.repeater.data.grid.AbstractDataGridView.populateItem(AbstractDataGridView.java:187)
at org.apache.wicket.markup.repeater.RefreshingView$1.newItem(RefreshingView.java:114)
at org.apache.wicket.markup.repeater.ReuseIfModelsEqualStrategy$1.next(ReuseIfModelsEqualStrategy.java:84)
at org.apache.wicket.markup.repeater.ReuseIfModelsEqualStrategy$1.next(ReuseIfModelsEqualStrategy.java:96)
at org.apache.wicket.markup.repeater.RefreshingView.addItems(RefreshingView.java:189)
at org.apache.wicket.markup.repeater.RefreshingView.onPopulate(RefreshingView.java:98)
at org.apache.wicket.markup.repeater.AbstractRepeater.onBeforeRender(AbstractRepeater.java:131)
at org.apache.wicket.markup.repeater.AbstractPageableView.onBeforeRender(AbstractPageableView.java:121)
at org.apache.wicket.Component.internalBeforeRender(Component.java:1061)
at org.apache.wicket.Component.beforeRender(Component.java:1095)
at org.apache.wicket.MarkupContainer.onBeforeRenderChildren(MarkupContainer.java:1727)
... 57 more