As reported Nikola Sobadjiev on Github:
I encountered the following exception:
in the following scenario:
A client disconnects ungracefully
The same client then reconnects and tries to resume its session via stream management
Openfire starts the process of resuming and tries to create a JID for that client here:
fullJid = new JID(authToken.getUsername(), authToken.getDomain(), resource, true);
However, getDomain is a deprecated method that looks at the xmpp.domain system property, which is null.
This property is being deleted by XMPPServer because the value in the XML configuration should be used instead.
I opted to use session.getServerName() because the session is already available there, had the most recent and correct data and in fact, the same method is used in many other places to the same effect.