PubSubModule.getItems() thows NullPointerException

I'm having an internal-server-error when I try to get the list of pubsub nodes.

Here is part of the trace :

2014.07.29 15:59:48 org.jivesoftware.openfire.pubsub.PubSubModule - Internal server error

java.lang.NullPointerException

at org.jivesoftware.openfire.pubsub.PubSubModule.getItems(PubSubModule.java:665)

at org.jivesoftware.openfire.disco.IQDiscoItemsHandler.handleIQ(IQDiscoItemsHandle r.java:131)

at org.jivesoftware.openfire.pubsub.PubSubModule.process(PubSubModule.java:209)

at org.jivesoftware.openfire.pubsub.PubSubModule.process(PubSubModule.java:168)

It's likely because I have no more nodes but I would have preferred to get null when I call discoverNodes().