Race condition when collecting presence of other sessions for the same user
When a resource connects, it is sent the presence information of all other connected resources of the same user. This occurs in `org.jivesoftware.openfire.SessionManager#broadcastPresenceOfOtherResource`
An exception has been logged by this code, that suggests that there's a race condition. The code first gets all addresses of the user, then, per address, finds a session. If between those calls a route gets removed, a nullpointerexception can occur (as the code assumes that the session will be non-null).
Something similar happens in org.jivesoftware.openfire.SessionManager#getSessions(java.lang.String)