org.apache.wicket.WicketRuntimeException: Error attaching this container for rendering: [SortGradeItemsByCategoryPanel [Component id = panel]] at org.apache.wicket.MarkupContainer.onBeforeRenderChildren(MarkupContainer.java:1699) at org.apache.wicket.Component.onBeforeRender(Component.java:3834) at org.apache.wicket.Component.internalBeforeRender(Component.java:949) at org.apache.wicket.Component.beforeRender(Component.java:1017) at org.apache.wicket.MarkupContainer.onBeforeRenderChildren(MarkupContainer.java:1687) at org.apache.wicket.Component.onBeforeRender(Component.java:3834) at org.apache.wicket.extensions.markup.html.tabs.TabbedPanel.onBeforeRender(TabbedPanel.java:266) at org.apache.wicket.Component.internalBeforeRender(Component.java:949) at org.apache.wicket.Component.beforeRender(Component.java:1017) at org.apache.wicket.MarkupContainer.onBeforeRenderChildren(MarkupContainer.java:1687) at org.apache.wicket.Component.onBeforeRender(Component.java:3834) at org.apache.wicket.markup.html.form.Form.onBeforeRender(Form.java:1803) at org.apache.wicket.Component.internalBeforeRender(Component.java:949) at org.apache.wicket.Component.beforeRender(Component.java:1017) at org.apache.wicket.MarkupContainer.onBeforeRenderChildren(MarkupContainer.java:1687) at org.apache.wicket.Component.onBeforeRender(Component.java:3834) at org.apache.wicket.Component.internalBeforeRender(Component.java:949) at org.apache.wicket.Component.beforeRender(Component.java:1017) at org.apache.wicket.MarkupContainer.onBeforeRenderChildren(MarkupContainer.java:1687) at org.apache.wicket.Component.onBeforeRender(Component.java:3834) at org.apache.wicket.extensions.ajax.markup.html.modal.ModalWindow.onBeforeRender(ModalWindow.java:859) at org.apache.wicket.Component.internalBeforeRender(Component.java:949) at org.apache.wicket.Component.beforeRender(Component.java:1017) at org.apache.wicket.Component.internalPrepareForRender(Component.java:2202) at org.apache.wicket.Component.prepareForRender(Component.java:2241) at org.apache.wicket.ajax.XmlAjaxResponse.writeComponent(XmlAjaxResponse.java:107) at org.apache.wicket.ajax.AbstractAjaxResponse.writeComponents(AbstractAjaxResponse.java:229) at org.apache.wicket.ajax.AbstractAjaxResponse.writeTo(AbstractAjaxResponse.java:154) at org.apache.wicket.ajax.AjaxRequestHandler.respond(AjaxRequestHandler.java:359) at org.apache.wicket.request.cycle.RequestCycle$HandlerExecutor.respond(RequestCycle.java:890) at org.apache.wicket.request.RequestHandlerStack.execute(RequestHandlerStack.java:64) at org.apache.wicket.request.RequestHandlerStack.execute(RequestHandlerStack.java:97) at org.apache.wicket.request.cycle.RequestCycle.execute(RequestCycle.java:261) at org.apache.wicket.request.cycle.RequestCycle.processRequest(RequestCycle.java:218) at org.apache.wicket.request.cycle.RequestCycle.processRequestAndDetach(RequestCycle.java:289) at org.apache.wicket.protocol.http.WicketFilter.processRequestCycle(WicketFilter.java:259) at org.apache.wicket.protocol.http.WicketFilter.processRequest(WicketFilter.java:201) at org.apache.wicket.protocol.http.WicketServlet.doGet(WicketServlet.java:137) at javax.servlet.http.HttpServlet.service(HttpServlet.java:634) at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.sakaiproject.util.RequestFilter.doFilter(RequestFilter.java:447) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:712) at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:459) at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:352) at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:312) at org.sakaiproject.tool.impl.ActiveToolComponent$MyActiveTool.forward(ActiveToolComponent.java:508) at org.sakaiproject.portal.charon.SkinnableCharonPortal.forwardTool(SkinnableCharonPortal.java:1526) at org.sakaiproject.portal.charon.handlers.SiteHandler.doSite(SiteHandler.java:499) at org.sakaiproject.portal.charon.handlers.SiteHandler.doGet(SiteHandler.java:296) at org.sakaiproject.portal.charon.handlers.SiteHandler.doGet(SiteHandler.java:184) at org.sakaiproject.portal.charon.SkinnableCharonPortal.doGet(SkinnableCharonPortal.java:870) at javax.servlet.http.HttpServlet.service(HttpServlet.java:634) at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.sakaiproject.util.RequestFilter.doFilter(RequestFilter.java:497) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:490) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:678) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408) at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:853) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1587) at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.base/java.lang.Thread.run(Thread.java:829) Caused by: java.lang.IllegalArgumentException: Comparison method violates its general contract! at java.base/java.util.TimSort.mergeLo(TimSort.java:781) at java.base/java.util.TimSort.mergeAt(TimSort.java:518) at java.base/java.util.TimSort.mergeForceCollapse(TimSort.java:461) at java.base/java.util.TimSort.sort(TimSort.java:254) at java.base/java.util.Arrays.sort(Arrays.java:1515) at java.base/java.util.ArrayList.sort(ArrayList.java:1750) at java.base/java.util.Collections.sort(Collections.java:179) at org.sakaiproject.gradebookng.tool.panels.SortGradeItemsByCategoryPanel$1.populateItem(SortGradeItemsByCategoryPanel.java:67) at org.apache.wicket.markup.html.list.ListView.onPopulate(ListView.java:523) at org.apache.wicket.markup.repeater.AbstractRepeater.onBeforeRender(AbstractRepeater.java:123) at org.apache.wicket.Component.internalBeforeRender(Component.java:949) at org.apache.wicket.Component.beforeRender(Component.java:1017) at org.apache.wicket.MarkupContainer.onBeforeRenderChildren(MarkupContainer.java:1687)