private synchronized Set<JID> doStopInbound() {
        return doStopInbound( null );
    }
The workhorse implementation of stopping inbound federation, that returns a list of JIDs representing the
occupants from the remote, joining nodes that are no longer in the room as a result of stopping the federation. For
these occupants, a presence stanza should be shared with the remainder of the occupants. It is desirable to send
these stanzas only after all any other nodes that are to be disconnected have been disconnected (to prevent
sharing updates with other remote nodes that we might also be disconnecting from. This method does
therefor not send these stanzas. Instead, it returns the addresses that should be send stanzas. This allows
callers to aggregate addresses, and send the stanzas in one iteration.

The implementation in this method will inform the remote, joining node that they left the local, joined node by
sending it a 'left' message.

@return The JIDs of occupants on the remote, joining node that are no longer in the room.
xmppserver/src/main/java/org/jivesoftware/openfire/muc/spi/FMUCHandler.java