NullPointerException with com.atlassian.jira.service.services.imap.ImapService

I have installed a "Create Issue" service handler to create issues from emails.

It's an IMAP account, so I used com.atlassian.jira.service.services.imap.ImapService.

Now everytime the service triggers I just see a NullPointerException in the log:

java.lang.NullPointerException
at com.atlassian.jira.project.AbstractProjectManager.isDefaultAssignee(AbstractProjectManager.java:135)
at com.atlassian.jira.project.AbstractProjectManager.isDefaultAssignee(AbstractProjectManager.java:130)
at com.atlassian.jira.project.AbstractProjectManager.getDefaultAssignee(AbstractProjectManager.java:165)
at com.atlassian.jira.service.util.handler.CreateIssueHandler.handleMessage(CreateIssueHandler.java:107)
at com.atlassian.jira.service.services.pop.PopService.run(PopService.java:110)
at com.atlassian.jira.service.JiraServiceContainer.run(JiraServiceContainer.java:51)
at com.atlassian.jira.service.ServiceRunner.execute(ServiceRunner.java:50)
at org.quartz.core.JobRunShell.run(JobRunShell.java:147)
at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:387)