NPE in JackRabbit ItemManager

20.04.2011 14:23:04 ERROR [org.apache.wicket.RequestCycle.logRuntimeException():1529]
java.lang.NullPointerException
at org.apache.jackrabbit.core.ItemManager.getDefinition(ItemManager.java:206)
at org.apache.jackrabbit.core.ItemSaveOperation.validateTransientItems(ItemSaveOperation.java:675)
at org.apache.jackrabbit.core.ItemSaveOperation.perform(ItemSaveOperation.java:216)
at org.apache.jackrabbit.core.session.SessionState.perform(SessionState.java:200)
at org.apache.jackrabbit.core.ItemImpl.perform(ItemImpl.java:91)
at org.apache.jackrabbit.core.ItemImpl.save(ItemImpl.java:329)
at org.apache.jackrabbit.core.session.SessionSaveOperation.perform(SessionSaveOperation.java:42)
at org.apache.jackrabbit.core.session.SessionState.perform(SessionState.java:200)
at org.apache.jackrabbit.core.SessionImpl.perform(SessionImpl.java:359)
at org.apache.jackrabbit.core.SessionImpl.save(SessionImpl.java:762)
at org.hippoecm.repository.decorating.SessionDecorator.save(SessionDecorator.java:204)
at org.hippoecm.repository.impl.SessionDecorator.save(SessionDecorator.java:185)
at org.hippoecm.repository.decorating.checked.SessionDecorator.save(SessionDecorator.java:229)
at org.onehippo.forge.relateddocs.RelatedDocCollection.add(RelatedDocCollection.java:150)
at org.onehippo.forge.relateddocs.editor.DocumentPickerDialog.onOk(DocumentPickerDialog.java:242)
at org.hippoecm.frontend.dialog.AbstractDialog.handleSubmit(AbstractDialog.java:580)
at org.hippoecm.frontend.dialog.AbstractDialog$3.onSubmit(AbstractDialog.java:430)
at org.hippoecm.frontend.dialog.AbstractDialog$ButtonWrapper$1.onSubmit(AbstractDialog.java:251)
at org.apache.wicket.ajax.markup.html.form.AjaxButton$1.onSubmit(AjaxButton.java:101)
at org.apache.wicket.ajax.form.AjaxFormSubmitBehavior.onEvent(AjaxFormSubmitBehavior.java:143)
at org.apache.wicket.ajax.AjaxEventBehavior.respond(AjaxEventBehavior.java:177)
at org.apache.wicket.ajax.AbstractDefaultAjaxBehavior.onRequest(AbstractDefaultAjaxBehavior.java:302)
at org.apache.wicket.request.target.component.listener.BehaviorRequestTarget.processEvents(BehaviorRequestTarget.java:157)
at org.apache.wicket.request.AbstractRequestCycleProcessor.processEvents(AbstractRequestCycleProcessor.java:92)
at org.hippoecm.frontend.PluginRequestCycleProcessor.processEvents(PluginRequestCycleProcessor.java:95)

In the re-run: a similar error was shown in my browser window:
java.lang.NullPointerException
org.apache.jackrabbit.core.ItemManager.getDefinition(ItemManager.java:206)
org.apache.jackrabbit.core.ItemSaveOperation.validateTransientItems(ItemSaveOperation.java:675)
org.apache.jackrabbit.core.ItemSaveOperation.perform(ItemSaveOperation.java:216)
org.apache.jackrabbit.core.session.SessionState.perform(SessionState.java:200)
org.apache.jackrabbit.core.ItemImpl.perform(ItemImpl.java:91)
org.apache.jackrabbit.core.ItemImpl.save(ItemImpl.java:329)
org.apache.jackrabbit.core.session.SessionSaveOperation.perform(SessionSaveOperation.java:42)
org.apache.jackrabbit.core.session.SessionState.perform(SessionState.java:200)
org.apache.jackrabbit.core.SessionImpl.perform(SessionImpl.java:359)
org.apache.jackrabbit.core.SessionImpl.save(SessionImpl.java:762)
org.hippoecm.repository.decorating.SessionDecorator.save(SessionDecorator.java:204)
org.hippoecm.repository.impl.SessionDecorator.save(SessionDecorator.java:185)
org.hippoecm.repository.decorating.checked.SessionDecorator.save(SessionDecorator.java:229)
org.hippoecm.frontend.model.JcrSessionModel.flush(JcrSessionModel.java:74)
org.hippoecm.frontend.model.JcrSessionModel.detach(JcrSessionModel.java:123)
org.hippoecm.frontend.session.UserSession.releaseJcrSession(UserSession.java:209)
org.hippoecm.frontend.session.UserSession.unbind(UserSession.java:344)
org.hippoecm.frontend.session.UnbindingHttpSessionStore.onUnbind(UnbindingHttpSessionStore.java:81)
org.apache.wicket.protocol.http.AbstractHttpSessionStore.unbind(AbstractHttpSessionStore.java:281)
org.apache.wicket.protocol.http.AbstractHttpSessionStore$SessionBindingListener.valueUnbound(AbstractHttpSessionStore.java:97)
org.apache.catalina.session.StandardSession.removeAttributeInternal(StandardSession.java:1676)
org.apache.catalina.session.StandardSession.expire(StandardSession.java:791)
org.apache.catalina.session.StandardSession.expire(StandardSession.java:643)
org.apache.catalina.session.StandardSession.invalidate(StandardSession.java:1148)
org.apache.catalina.session.StandardSessionFacade.invalidate(StandardSessionFacade.java:150)
org.hippoecm.frontend.plugins.login.ConcurrentLoginFilter.doFilter(ConcurrentLoginFilter.java:51)