RS if a task is deleted but still use

RedScreen on test8 10.4a
2015-06-22 18:06:36,558 [ajp-bio-8028-exec-6] ERROR OLATRuntimeException - OLAT::ERROR ^%^ N8-E1

Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:38.0) Gecko/20100101 Firefox/38.0

**RedScreen**

<dispatchinfo>
	<componentinfo>	
		<compname>ffo_main_barebone</compname>
		<compclass>org.olat.core.gui.components.form.flexible.impl.FormWrapperContainer</compclass>
		<extendedinfo>n/a</extendedinfo>
		<event>
			<class&gt;org.olat.core.gui.components.form.flexible.impl.elements.table.SelectionEvent</class&gt;
			<command>select</command>
			<tostring>com:select,org.olat.core.gui.components.form.flexible.impl.elements.table.SelectionEvent@c9ff351b</tostring>
		</event>
	</componentinfo>
	<controllerinfo>
		<controllername>org.olat.course.nodes.gta.ui.GTACoachedParticipantListController</controllername>
		<controllername>org.olat.course.nodes.gta.ui.GTACoachSelectionController</controllername>
		<controllername>org.olat.course.nodes.gta.ui.GTARunController</controllername>
		<controllername>org.olat.course.run.RunMainController</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.doGet(OpenOLATServlet.java:209)
   at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
>>> stack of 2.cause::java.lang.NullPointerException: null
-> at org.olat.course.nodes.gta.ui.GTAAssignedTaskController.<init>(GTAAssignedTaskController.java:90)
   at org.olat.course.nodes.gta.ui.GTACoachController.stepAssignment(GTACoachController.java:154)
   at org.olat.course.nodes.gta.ui.GTAAbstractController.process(GTAAbstractController.java:166)
   at org.olat.course.nodes.gta.ui.GTAAbstractController.<init>(GTAAbstractController.java:139)
   at org.olat.course.nodes.gta.ui.GTACoachController.<init>(GTACoachController.java:108)
   at org.olat.course.nodes.gta.ui.GTACoachController.<init>(GTACoachController.java:92)
   at org.olat.course.nodes.gta.ui.GTACoachSelectionController.doSelectParticipant(GTACoachSelectionController.java:167)
   at org.olat.course.nodes.gta.ui.GTACoachSelectionController.event(GTACoachSelectionController.java:126)
   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)