private void updateNonPersistentRoomStat(@Nullable final MUCRoom oldValue, @Nullable final MUCRoom newValue)
    {
        int delta = 0;
        if (oldValue != null && !oldValue.isPersistent()) {
            delta--;
        }
        if (newValue != null && !newValue.isPersistent()) {
            delta++;
        }
        if (delta < 0) {
            decrementStatistic(STAT_KEY_ROOMCOUNT_NONPERSISTENT);
        } else if (delta > 0) {
            incrementStatistic(STAT_KEY_ROOMCOUNT_NONPERSISTENT);
        }
    }
Modifies the statistic in {@link #ROOM_CACHE_STATS} that keeps a count of all non-persisted MUC rooms
(key: {@link #STAT_KEY_ROOMCOUNT_NONPERSISTENT}), based on a rooms that are removed from or added to {@link #ROOM_CACHE}

@param oldValue a room that was removed from {@link #ROOM_CACHE}
@param newValue a room that was added to {@link #ROOM_CACHE}
xmppserver/src/main/java/org/jivesoftware/openfire/muc/spi/LocalMUCRoomManager.java