When I start a workflow, particpants don't get mail notification and the log get this error :

2013-08-26 12:24:24,357 ERROR [org.nuxeo.ecm.platform.ec.notification.NotificationEventListener] Error during Notification processing for event workflowTaskAssigned java.lang.NullPointerException

    at org.nuxeo.ecm.core.security.SecurityService.checkPermission(SecurityService.java:136)
    at org.nuxeo.ecm.core.api.AbstractSession.hasPermission(AbstractSession.java:449)
    at org.nuxeo.ecm.core.api.AbstractSession.hasPermission(AbstractSession.java:440)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.nuxeo.ecm.core.api.TransactionalCoreSessionWrapper.invoke(TransactionalCoreSessionWrapper.java:133)
    at com.sun.proxy.$Proxy43.hasPermission(Unknown Source)
    at org.nuxeo.ecm.platform.ec.notification.NotificationEventListener.sendNotificationSignalForUser(NotificationEventListener.java:221)
    at org.nuxeo.ecm.platform.ec.notification.NotificationEventListener.handleNotifications(NotificationEventListener.java:192)
    at org.nuxeo.ecm.platform.ec.notification.NotificationEventListener.handleEvent(NotificationEventListener.java:108)
    at org.nuxeo.ecm.core.event.impl.AsyncEventExecutor$ListenerWork.work(AsyncEventExecutor.java:153)
    at org.nuxeo.ecm.core.work.AbstractWork.run(AbstractWork.java:150)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:724)

I use Nuxeo 5.6-HF22 with LDAP authentication. With Nuxeo 5.6-HF17, notifications for workflow worked well.

Is there a workaround ?