RS upgrade old task element if user was deleted but its task not cleaned up

2015-11-10 17:52:06,372 [ajp-bio-8006-exec-971] ERROR OLATRuntimeException - OLAT::ERROR ^%^ N1-E5951 ^%^ org.olat.core.logging 

Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Firefox/31.0 ^%^ **RedScreen**

<dispatchinfo>
	<componentinfo>
		<compname>ffo_main_null</compname>
		<compclass>org.olat.core.gui.components.form.flexible.impl.FormWrapperContainer</compclass>
		<extendedinfo>n/a</extendedinfo>
		<event>
			<class&gt;org.olat.core.gui.control.Event</class&gt;
			<command>validation ok</command>
			<tostring>com:validation ok,org.olat.core.gui.control.Event@d62b3f02</tostring>
		</event>
	</componentinfo>
	<controllerinfo>
		<controllername>org.olat.course.editor.AlternativeCourseNodeController</controllername>
		<controllername>org.olat.course.editor.EditorMainController</controllername>
		<controllername>org.olat.course.run.CourseRuntimeController</controllername>
		<controllername>org.olat.core.commons.fullWebApp.BaseFullWebappController</controllername>
	</controllerinfo>
</dispatchinfo>

>>> stack of 1.cause::org.olat.core.logging.OLATRuntimeException: null
-> at org.olat.core.gui.exception.ExceptionWindowController.<init>(ExceptionWindowController.java:116)
   at org.olat.core.gui.exception.MsgFactory.createMessageChiefController(MsgFactory.java:57)
   at org.olat.core.gui.exception.MsgFactory.createMessageChiefController(MsgFactory.java:46)
   at org.olat.core.gui.components.Window.dispatchRequest(Window.java:536)
   at org.olat.core.gui.components.Window.doDispatchRequest(Window.java:234)
   at org.olat.core.gui.components.AbstractComponent.dispatchRequest(AbstractComponent.java:193)
   at org.olat.dispatcher.AuthenticatedDispatcher.processValidDispatchURI(AuthenticatedDispatcher.java:245)
   at org.olat.dispatcher.AuthenticatedDispatcher.execute(AuthenticatedDispatcher.java:201)
   at org.olat.core.servlets.OpenOLATServlet.executeUserRequest(OpenOLATServlet.java:280)
   at org.olat.core.servlets.OpenOLATServlet.doPost(OpenOLATServlet.java:223)
   at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
>>> stack of 2.cause::java.lang.NullPointerException: null
-> at org.olat.course.nodes.gta.manager.GTAManagerImpl.getSubmitContainer(GTAManagerImpl.java:162)
   at org.olat.course.nodes.ta.ConvertToGTACourseNode.convertDropbox(ConvertToGTACourseNode.java:170)
   at org.olat.course.nodes.ta.ConvertToGTACourseNode.convert(ConvertToGTACourseNode.java:106)
   at org.olat.course.nodes.TACourseNode.copyConfigurationTo(TACourseNode.java:778)
   at org.olat.course.editor.EditorMainController.doCreateAlternateBuildingBlock(EditorMainController.java:450)
   at org.olat.course.editor.EditorMainController.event(EditorMainController.java:710)
   at org.olat.core.gui.control.DefaultController$1.run(DefaultController.java:246)
   at org.olat.core.logging.activity.ThreadLocalUserActivityLoggerInstaller.runWithUserActivityLogger(ThreadLocalUserActivityLoggerInstaller.java:108)
   at org.olat.core.gui.control.DefaultController.dispatchEvent(DefaultController.java:243)
   at org.olat.core.gui.control.DefaultController.fireEvent(DefaultController.java:190)
   at org.olat.course.editor.AlternativeCourseNodeController.formOK(AlternativeCourseNodeController.java:115)