A custom Priority Icon URL of just / breaks outgoing mail notifications

2014-04-06 07:39:11,571 Sending mailitem com.atlassian.jira.mail.IssueMailQueueItem@1afb379[issue=com.atlassian.jira.issue.IssueImpl@382b7f[id=11801,summary=Test Issue,key=TEST-61,created=2014-04-06 07:38:34.685,updated=2014-04-06 07:38:34.685,assignee=<null>,reporter=sysadmin:10000],remoteUser=sysadmin:10000,notificationType=Project_Lead,eventTypeId=1,templateId=1] ERROR ServiceRunner    Mail Queue Service [atlassian.jira.mail.MailingListCompiler] Failed adding mail for notification recipient: [email=noreply@atlassian.com, user=testUser:10000]
java.lang.NullPointerException
at org.apache.commons.io.IOUtils.copyLarge(IOUtils.java:1025)
at org.apache.commons.io.IOUtils.copy(IOUtils.java:999)
at com.atlassian.jira.mail.util.ByteArrayDataSource.<init>(ByteArrayDataSource.java:42)
at com.atlassian.jira.mail.util.MailAttachmentsManagerImpl$ImageAttachment.buildBodyPart(MailAttachmentsManagerImpl.java:219)
at com.atlassian.jira.mail.util.MailAttachmentsManagerImpl$1.apply(MailAttachmentsManagerImpl.java:167)
at com.atlassian.jira.mail.util.MailAttachmentsManagerImpl$1.apply(MailAttachmentsManagerImpl.java:163)
at com.google.common.collect.Iterators$8.next(Iterators.java:782)
at com.google.common.collect.Iterators$7.computeNext(Iterators.java:644)
at com.google.common.collect.AbstractIterator.tryToComputeNext(AbstractIterator.java:141)
at com.google.common.collect.AbstractIterator.hasNext(AbstractIterator.java:136)
at com.google.common.collect.Iterators$5.hasNext(Iterators.java:539)
at com.atlassian.jira.mail.builder.EmailRenderer.buildMailWithAttachments(EmailRenderer.java:150)
at com.atlassian.jira.mail.builder.EmailRenderer.renderEmailBody(EmailRenderer.java:122)
at com.atlassian.jira.mail.builder.EmailRenderer.render(EmailRenderer.java:165)
at com.atlassian.jira.mail.builder.EmailBuilder.renderNow(EmailBuilder.java:162)
at com.atlassian.jira.mail.builder.EmailBuilder.renderNowAsQueueItem(EmailBuilder.java:152)
at com.atlassian.jira.mail.MailingListCompiler$1.processRecipient(MailingListCompiler.java:306)
at com.atlassian.jira.mail.NotificationRecipientProcessor.process(NotificationRecipientProcessor.java:39)
at com.atlassian.jira.mail.MailingListCompiler.addMailsToQueue(MailingListCompiler.java:331)
at com.atlassian.jira.mail.MailingListCompiler.access$200(MailingListCompiler.java:46)
at com.atlassian.jira.mail.MailingListCompiler$NotificationCompiler.addEmailsToQueue(MailingListCompiler.java:454)
at com.atlassian.jira.mail.MailingListCompiler$NotificationCompiler.sendLists(MailingListCompiler.java:424)
at com.atlassian.jira.mail.MailingListCompiler$NotificationCompiler.sendNoLevelsIgnoreGroup(MailingListCompiler.java:404)
at com.atlassian.jira.mail.MailingListCompiler$NotificationCompiler.sendToAll(MailingListCompiler.java:399)
at com.atlassian.jira.mail.MailingListCompiler.sendLists(MailingListCompiler.java:144)
at com.atlassian.jira.mail.IssueMailQueueItem.send(IssueMailQueueItem.java:149)
at com.atlassian.mail.queue.MailQueueImpl.sendBuffer(MailQueueImpl.java:66)
at com.atlassian.jira.service.services.mail.MailQueueService.run(MailQueueService.java:27)
at com.atlassian.jira.service.JiraServiceContainerImpl.run(JiraServiceContainerImpl.java:65)
at com.atlassian.jira.service.ServiceRunner.runService(ServiceRunner.java:75)
at com.atlassian.jira.service.ServiceRunner.runServiceId(ServiceRunner.java:53)
at com.atlassian.jira.service.ServiceRunner.runJob(ServiceRunner.java:36)
at com.atlassian.scheduler.core.JobLauncher.runJob(JobLauncher.java:121)
at