Openfire 4.0.2 MultiUserChatServiceImpl NullPointerException

Hi,

Recently upgraded to Openfire 4.0.2, and every hour I get an exception in MultiUserChatServiceImpl when it runs the cleanup task to remove unused rooms from memory.

Here is the exception:

2016.05.12 06:20:27 org.jivesoftware.openfire.muc.spi.MultiUserChatServiceImpl - Internal server error

java.lang.NullPointerException

at org.jivesoftware.openfire.muc.spi.MultiUserChatServiceImpl.removeChatRoom(Multi UserChatServiceImpl.java:769)

at org.jivesoftware.openfire.muc.spi.MultiUserChatServiceImpl.removeChatRoom(Multi UserChatServiceImpl.java:742)

at org.jivesoftware.openfire.muc.spi.MultiUserChatServiceImpl.cleanupRooms(MultiUs erChatServiceImpl.java:613)

at org.jivesoftware.openfire.muc.spi.MultiUserChatServiceImpl.access$400(MultiUser ChatServiceImpl.java:106)

at org.jivesoftware.openfire.muc.spi.MultiUserChatServiceImpl$CleanupTask.run(Mult iUserChatServiceImpl.java:602)

I can see the rooms loaded in the admin page, so any idea what could be causing this?

Thanks,

Joao