Verbose logging when filter subscription sends to nonexistent group

When a group is subscribed to the filter, and then that group is deleted, the filtersubscription still exists, and once a minute the logs get filled with these errors:

2007-06-18 12:46:04,585 Sending mailitem com.atlassian.jira.mail.SubscriptionMailQueueItem subject: 'Subscription: testfilter' Owner: 'test ERROR [atlassian.mail.queue.MailQueueImpl] Error occurred in sending e-mail: com.atlassian.jira.mail.SubscriptionMailQueueItem subject: 'Subscription: testfilter' Owner: 'test
com.atlassian.mail.MailException: com.opensymphony.user.EntityNotFoundException: No group testgroup found
at com.atlassian.jira.mail.SubscriptionMailQueueItem.send(SubscriptionMailQueueItem.java:88)
at com.atlassian.mail.queue.MailQueueImpl.sendBuffer(MailQueueImpl.java:68)
at com.atlassian.jira.service.services.mail.MailQueueService.run(MailQueueService.java:23)
at com.atlassian.jira.service.JiraServiceContainerImpl.run(JiraServiceContainerImpl.java:67)
at com.atlassian.jira.service.ServiceRunner.execute(ServiceRunner.java:48)
at org.quartz.core.JobRunShell.run(JobRunShell.java:191)
at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:516)
Caused by: com.opensymphony.user.EntityNotFoundException: No group testgroup found
at com.opensymphony.user.UserManager.getEntity(UserManager.java:302)
at com.opensymphony.user.UserManager.getGroup(UserManager.java:172)
at com.atlassian.jira.mail.SubscriptionMailQueueItem.send(SubscriptionMailQueueItem.java:71)
... 6 more
2007-06-18 12:46:04,585 Sending mailitem com.atlassian.jira.mail.SubscriptionMailQueueItem subject: 'Subscription: testfilter' Owner: 'test ERROR [atlassian.jira.mail.SubscriptionMailQueueItem] com.opensymphony.user.EntityNotFoundException: No group testgroup found
com.opensymphony.user.EntityNotFoundException: No group testgroup found
at com.opensymphony.user.UserManager.getEntity(UserManager.java:302)
at com.opensymphony.user.UserManager.getGroup(UserManager.java:172)
at com.atlassian.jira.mail.SubscriptionMailQueueItem.send(SubscriptionMailQueueItem.java:71)
at com.atlassian.mail.queue.MailQueueImpl.sendBuffer(MailQueueImpl.java:68)
at com.atlassian.jira.service.services.mail.MailQueueService.run(MailQueueService.java:23)
at com.atlassian.jira.service.JiraServiceContainerImpl.run(JiraServiceContainerImpl.java:67)
at com.atlassian.jira.service.ServiceRunner.execute(ServiceRunner.java:48)
at org.quartz.core.JobRunShell.run(JobRunShell.java:191)
at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:516)

Assuming that this is not an error condition (that it's okay to have dangling group pointers in filtersubscriptions), we should a) log it as WARN, not ERROR, b) print a one-line message, rather than a stacktrace.