The error message is as follows:

Cause:
java.lang.NullPointerException

Stack Trace: [hide]

java.lang.NullPointerException
at
com.atlassian.confluence.mail.template.MailNotificationQueueItem.createFromTemplateFile(MailNotificationQueueItem.java:55)
at
com.atlassian.confluence.event.notifiers.EMailNotifier.queueNotification(EMailNotifier.java:150)
at
com.atlassian.confluence.event.notifiers.EMailNotifier.onEvent(EMailNotifier.java:111)
at
com.atlassian.confluence.event.EventNotifierInterceptor.after(EventNotifierInterceptor.java:53)
at
com.opensymphony.xwork.interceptor.AroundInterceptor.intercept(AroundInterceptor.java:35)
at
com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:163)