Invisible RS: rare timing issue with the auto save feature of QTI 2.1

2017-09-22 09:04:37,047 [ajp-nio2-8026-exec-678] ERROR OLATRuntimeException - OLAT::ERROR ^%^ N26-E183 ^%^ org.olat.core.logging
https://xz.olat.com/auth/RepositoryEntry/116850700/CourseNode/96048429321601/test/0
Mozilla/5.0 (iPhone; CPU iPhone OS 10_3_3 like Mac OS X) AppleWebKit/603.3.8 (KHTML, like Gecko) Version/10.0 Mobile/14G60 Safari/602.1
**RedScreen**

<dispatchinfo>
	<componentinfo>
		<compname>ffo_main_at_run</compname>
		<compclass>org.olat.core.gui.components.form.flexible.impl.FormWrapperContainer</compclass>
		<extendedinfo>n/a</extendedinfo>
		<event>
			<class&gt;org.olat.ims.qti21.ui.QTIWorksAssessmentTestEvent</class&gt;
			<command>tmpResponse</command>
			<tostring>com:tmpResponse,org.olat.ims.qti21.ui.QTIWorksAssessmentTestEvent@48683297</tostring>
		</event>
	</componentinfo>
	<controllerinfo>
		<controllername>org.olat.ims.qti21.ui.AssessmentTestDisplayController$QtiWorksController</controllername>
		<controllername>org.olat.ims.qti21.ui.AssessmentTestDisplayController</controllername>
		<controllername>org.olat.course.nodes.iq.QTI21AssessmentRunController</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:549)
   at org.olat.core.gui.components.Window.doDispatchRequest(Window.java:242)
   at org.olat.core.gui.components.AbstractComponent.dispatchRequest(AbstractComponent.java:193)
   at org.olat.dispatcher.AuthenticatedDispatcher.processValidDispatchURI(AuthenticatedDispatcher.java:273)
   at org.olat.dispatcher.AuthenticatedDispatcher.execute(AuthenticatedDispatcher.java:190)
   at org.olat.core.servlets.OpenOLATServlet.executeUserRequest(OpenOLATServlet.java:292)
   at org.olat.core.servlets.OpenOLATServlet.doPost(OpenOLATServlet.java:235)
   at javax.servlet.http.HttpServlet.service(HttpServlet.java:648)
>>> stack of 2.cause::java.lang.NullPointerException: null
-> at org.olat.ims.qti21.ui.AssessmentTestDisplayController.handleTemporaryResponse(AssessmentTestDisplayController.java:939)
   at org.olat.ims.qti21.ui.AssessmentTestDisplayController.processQTIEvent(AssessmentTestDisplayController.java:644)
   at org.olat.ims.qti21.ui.AssessmentTestDisplayController.event(AssessmentTestDisplayController.java:459)
   at org.olat.core.gui.control.DefaultController$1.run(DefaultController.java:246)
   at org.olat.core.logging.activity.ThreadLocalUserActivityLoggerInstaller.runWithUserActivityLogger(ThreadLocalUserActivityLoggerInstaller.java:108)
   at org.olat.core.gui.control.DefaultController.dispatchEvent(DefaultController.java:243)
   at org.olat.core.gui.control.DefaultController.fireEvent(DefaultController.java:190)
   at org.olat.core.gui.components.form.flexible.impl.FormBasicController.fireEvent(FormBasicController.java:711)
   at org.olat.ims.qti21.ui.AssessmentTestDisplayController$QtiWorksController.fireTemporaryResponse(AssessmentTestDisplayController.java:1904)
   at org.olat.ims.qti21.ui.AbstractQtiWorksController.processTemporaryResponse(AbstractQtiWorksController.java:134)
   at org.olat.ims.qti21.ui.AssessmentTestDisplayController$QtiWorksController.formInnerEvent(AssessmentTestDisplayController.java:1871)