Course coach try to open a group task element in assessment tool

Error code: N8-E2 Last business path: https://testing.frentix.com/test8/url/RepositoryEntry/404062208/assessmentToolv2/0/Users/0/Node/94797670744252

Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/54.0.2840.98 Safari/537.36 ^%^ ExceptionWindowController: Throwable occurred, logging the full stacktrace:
>>>stack of 1.cause::java.lang.NullPointerException: null
-> at org.olat.course.nodes.gta.manager.GTAManagerImpl.filterBusinessGroups(GTAManagerImpl.java:502)
   at org.olat.course.nodes.GTACourseNode.getCoachedGroupListController(GTACourseNode.java:851)
   at org.olat.course.assessment.ui.tool.AssessmentIdentityListCourseTreeController.doSelectCourseNode(AssessmentIdentityListCourseTreeController.java:170)
   at org.olat.course.assessment.ui.tool.AssessmentIdentityListCourseTreeController.event(AssessmentIdentityListCourseTreeController.java:144)
   at org.olat.core.gui.control.DefaultController.dispatchEvent(DefaultController.java:202)
   at org.olat.core.gui.components.AbstractComponent$1.run(AbstractComponent.java:240)
   at org.olat.core.logging.activity.ThreadLocalUserActivityLoggerInstaller.runWithUserActivityLogger(ThreadLocalUserActivityLoggerInstaller.java:108)
   at org.olat.core.gui.components.AbstractComponent.fireEvent(AbstractComponent.java:238)
   at org.olat.core.gui.components.tree.MenuTree.handleClick(MenuTree.java:300)
   at org.olat.core.gui.components.tree.MenuTree.doDispatchRequest(MenuTree.java:199)
   at org.olat.core.gui.components.AbstractComponent.dispatchRequest(AbstractComponent.java:193)