Audit migration from SQL to Elasticsearch doesn't work when using a Redis backend

2015-10-12 14:23:12,668 WARN  [localhost-startStop-1] [org.nuxeo.elasticsearch.core.ElasticSearchAdminImpl] Initializing index: audit, type: entry with dropIfExists flag, deleting an existing index
2015-10-12 14:23:13,545 ERROR [localhost-startStop-1] [org.nuxeo.ecm.core.redis.contribs.RedisBlockingQueue] Failed to add Work: (, Progress(?%, ?/0), null)
java.io.NotSerializableException: org.nuxeo.elasticsearch.audit.ESAuditBackend
        at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1184)
        at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
        at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1509)
        at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
        at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
        at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:348)
        at org.nuxeo.ecm.core.redis.contribs.RedisWorkQueuing.serializeWork(Redis...