Mail Queue stuck on upgrade

See stack trace:

2003-08-20 11:17:22,506 ERROR [atlassian.jira.mail.IssueMailQueueItem]
null
java.lang.NumberFormatException: null
at java.lang.Integer.parseInt(Integer.java:436)
at java.lang.Integer.parseInt(Integer.java:518)
at
com.atlassian.jira.mail.IssueMailQueueItem.getIssueContextParams(IssueMa
ilQueueItem.java:151)
at
com.atlassian.jira.mail.IssueMailQueueItem.send(IssueMailQueueItem.java:
104)
at
com.atlassian.jira.mail.MailQueueImpl.sendBuffer(MailQueueImpl.java:52)
at
com.atlassian.jira.service.services.mail.MailQueueService.run(MailQueueS
ervice.java:25)
at
com.atlassian.jira.service.JiraServiceContainer.run(JiraServiceContainer
.java:54)
at
com.atlassian.jira.service.ServiceRunner.execute(ServiceRunner.java:53)
at org.quartz.core.JobRunShell.run(JobRunShell.java:147)
at
org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java
:387)

Perhaps we use 'defaultBackedString' and have a default in the properties file?