NullPointerException when clicking on [...] besides "Content path" in URL designer

In URL designer, if you click on [...] to select the content path, the expected popup is not shown and the following stacktrace appears in the logs:

24.02.2010 15:39:08 ERROR [org.apache.wicket.RequestCycle.logRuntimeException():1521]
java.lang.NullPointerException
at org.hippoecm.frontend.editor.plugins.linkpicker.LinkPickerDialog.createContentPanel(LinkPickerDialog.java:150)
at org.hippoecm.frontend.editor.plugins.linkpicker.LinkPickerDialog.<init>(LinkPickerDialog.java:74)
at org.hippoecm.hst.plugins.frontend.editor.dialogs.HstPickerDialog.<init>(HstPickerDialog.java:42)
at org.hippoecm.hst.plugins.frontend.editor.dialogs.HstContentPickerDialog.<init>(HstContentPickerDialog.java:42)
at org.hippoecm.hst.plugins.frontend.editor.sitemap.SitemapItemEditorPlugin$1$1.<init>(SitemapItemEditorPlugin.java:99)
at org.hippoecm.hst.plugins.frontend.editor.sitemap.SitemapItemEditorPlugin$1.createDialog(SitemapItemEditorPlugin.java:99)
at org.hippoecm.hst.plugins.frontend.editor.sitemap.SitemapItemEditorPlugin$1.createDialog(SitemapItemEditorPlugin.java:93)
at org.hippoecm.frontend.dialog.DialogAction.execute(DialogAction.java:35)
at org.hippoecm.frontend.dialog.DialogLink$1.onClick(DialogLink.java:45)
at org.apache.wicket.ajax.markup.html.AjaxLink$1.onEvent(AjaxLink.java:68)
at org.apache.wicket.ajax.AjaxEventBehavior.respond(AjaxEventBehavior.java:177)
at org.apache.wicket.ajax.AbstractDefaultAjaxBehavior.onRequest(AbstractDefaultAjaxBehavior.java:299)
at org.apache.wicket.request.target.component.listener.BehaviorRequestTarget.processEvents(BehaviorRequestTarget.java:119)
at org.apache.wicket.request.AbstractRequestCycleProcessor.processEvents(AbstractRequestCycleProcessor.java:92)
at org.hippoecm.frontend.PluginRequestCycleProcessor.processEvents(PluginRequestCycleProcessor.java:31)
at org.apache.wicket.RequestCycle.processEventsAndRespond(RequestCycle.java:1250)
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:468)
at org.apache.wicket.protocol.http.WicketFilter.doFilter(WicketFilter.java:301)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.hippoecm.frontend.plugins.login.ConcurrentLoginFilter.doFilter(ConcurrentLoginFilter.java:54)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:849)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:454)
at java.lang.Thread.run(Thread.java:619)