RS: concurrent delete / edit of a question in question bank

2018-03-05 16:28:35,390 [ajp-nio2-8082-exec-1] ERROR OLATRuntimeException - OLAT::ERROR ^%^ N82-E1 ^%^ org.olat.core.logging 

https://xyz.ch/auth/QPool/0
Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; rv:11.0) like Gecko ^%^ **RedScreen**

<dispatchinfo>
	<componentinfo>
		<compname>ffo_main_item_list</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-item</command>
			<tostring>com:select-item,org.olat.core.gui.components.form.flexible.impl.elements.table.SelectionEvent@a122563</tostring>
		</event>
	</componentinfo>
	<controllerinfo>
		<controllername>org.olat.modules.qpool.ui.QuestionListController</controllername>
		<controllername>org.olat.modules.qpool.ui.QuestionPoolMainEditorController</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:589)
   at org.olat.core.gui.components.Window.doDispatchRequest(Window.java:282)
   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:289)
   at org.olat.core.servlets.OpenOLATServlet.doPost(OpenOLATServlet.java:232)
   at javax.servlet.http.HttpServlet.service(HttpServlet.java:661)
>>> stack of 2.cause::java.lang.NullPointerException: null
-> at org.olat.core.util.resource.OresHelper.createStringRepresenting(OresHelper.java:99)
   at org.olat.commons.coordinate.cluster.lock.ClusterLocker.acquireLock(ClusterLocker.java:100)
   at org.olat.modules.qpool.manager.QuestionPoolServiceImpl.acquireLock(QuestionPoolServiceImpl.java:282)
   at org.olat.modules.qpool.ui.QuestionItemDetailsController.<init>(QuestionItemDetailsController.java:155)
   at org.olat.modules.qpool.ui.QuestionListController.doOpenDetails(QuestionListController.java:1342)
   at org.olat.modules.qpool.ui.QuestionListController.doOpenDetails(QuestionListController.java:1327)
   at org.olat.modules.qpool.ui.QuestionListController.doSelect(QuestionListController.java:1321)
   at org.olat.modules.qpool.ui.AbstractItemListController.formInnerEvent(AbstractItemListController.java:298)
   at org.olat.modules.qpool.ui.QuestionListController.formInnerEvent(QuestionListController.java:360)
   at org.olat.core.gui.components.form.flexible.impl.FormBasicController.event(FormBasicController.java:421)
   at org.olat.modules.qpool.ui.QuestionListController.event(QuestionListController.java:405)