JIRA encounters problems when database transactions are rolled back

2016-11-21 10:47:10,665 http-nio-8080-exec-63 ERROR user session jsession ip,jirabaseurl/secure/CommentAssignIssue.jspa [c.a.event.internal.AsynchronousAbleEventDispatcher] There was an exception thrown trying to dispatch event [com.atlassian.jira.event.issue.IssueEvent@77b57e33[issue=issue-key,comment=<null>,worklog=<null>,changelog=[GenericEntity:ChangeGroup][issue,755181][author,user][created,2016-11-21 10:47:10.659][id,4687444],eventTypeId=2,sendMail=false,params={eventsource=action, baseurl=https://jirabaseurl},subtasksUpdated=true]] from the invoker [SingleParameterMethodListenerInvoker{method=public void com.atlassian.jira.event.listeners.mention.MentionEventListener.onIssueEvent(com.atlassian.jira.event.issue.IssueEvent), listener=com.atlassian.jira.event.listeners.mention.MentionEventListener@1a191982}]
java.lang.RuntimeException: java.lang.NullPointerException
	at com.atlassian.event.internal.SingleParameterMethodListenerInvoker.invoke(SingleParameterMethodListenerInvoker.java:50)
	at com.atlassian.event.internal.AsynchronousAbleEventDispatcher$1$1.run(AsynchronousAbleEventDispatcher.java:48)
	at com.google.common.util.concurrent.MoreExecutors$DirectExecutorService.execute(MoreExecutors.java:299)
	at com.atlassian.event.internal.AsynchronousAbleEventDispatcher.dispatch(AsynchronousAbleEventDispatcher.java:107)
	at com.atlassian.event.internal.EventPublisherImpl.invokeListeners(EventPublisherImpl.java:160)
	at com.atlassian.event.internal.EventPublisherImpl.publish(EventPublisherImpl.java:79)
	at com.atlassian.jira.event.issue.DefaultIssueEventManager.publishEvent(DefaultIssueEventManager.java:120)
	at com.atlassian.jira.event.issue.DefaultIssueEventManager.publishAsRedundant(DefaultIssueEventManager.java:132)
	at com.atlassian.jira.event.issue.DefaultIssueEventManager.dispatchRedundantEvent(DefaultIssueEventManager.java:103)
	at com.atlassian.jira.issue.util.DefaultIssueUpdater.storeModifiedFields(DefaultIssueUpdater.java:95)
	at com.atlassian.jira.issue.util.DefaultIssueUpdater.doUpdate(DefaultIssueUpdater.java:50)
	at com.atlassian.jira.issue.managers.DefaultIssueManager.doUpdate(DefaultIssueManager.java:721)
	at com.atlassian.jira.issue.managers.DefaultIssueManager.updateIssue(DefaultIssueManager.java:706)
	at com.atlassian.jira.issue.managers.DefaultIssueManager.updateIssue(DefaultIssueManager.java:686)
	at com.iamhuy.jira.plugin.workflow.AssignFromCustomfieldFunction.execute(AssignFromCustomfieldFunction.java:36)
	at com.opensymphony.workflow.AbstractWorkflow.executeFunction(AbstractWorkflow.java:1050)
	at com.opensymphony.workflow.AbstractWorkflow.transitionWorkflow(AbstractWorkflow.java:1446)
	at com.opensymphony.workflow.AbstractWorkflow.doAction(AbstractWorkflow.java:564)
	at com.atlassian.jira.workflow.OSWorkflowManager.doWorkflowActionInsideTxn(OSWorkflowManager.java:825)
	at com.atlassian.jira.workflow.OSWorkflowManager.doWorkflowAction(OSWorkflowManager.java:786)
	at com.atlassian.jira.bc.issue.DefaultIssueService.transition(DefaultIssueService.java:430)
	at com.atlassian.jira.web.action.issue.CommentAssignIssue.doExecute(CommentAssignIssue.java:164)
	... 1 filtered
	at com.atlassian.jira.action.JiraActionSupport.execute(JiraActionSupport.java:63)
	... 7 filtered
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
	... 50 filtered
	at com.atlassian.greenhopper.jira.filters.ClassicBoardRouter.doFilter(ClassicBoardRouter.java:59)
	... 50 filtered
	at com.almworks.jira.structure.services.IssueLinksInterceptor.doHttpFilter(IssueLinksInterceptor.java:98)
	at com.almworks.jira.structure.web.AbstractStructureServletFilter.doFilter(AbstractStructureServletFilter.java:34)
	... 104 filtered
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException
	at com.atlassian.jira.notification.DefaultNotificationSchemeManager.getRecipients(DefaultNotificationSchemeManager.java:335)
	at com.atlassian.jira.notification.DefaultNotificationSchemeManager.getRecipients(DefaultNotificationSchemeManager.java:368)
	at com.atlassian.jira.event.listeners.mention.MentionEventListener.onIssueEvent(MentionEventListener.java:39)
	at sun.reflect.GeneratedMethodAccessor1752.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at com.atlassian.event.internal.SingleParameterMethodListenerInvoker.invoke(SingleParameterMethodListenerInvoker.java:36)
	... 242 more