Add clearCompletedSessions please:

[renetik]

 static void clearCompletedSessions() {
        synchronized (sessionHistoryLock) {
            ArrayList<Session> completedSessions = new ArrayList<>();
            for (Session session : sessionHistoryList) {
                if (session.getState() == COMPLETED) completedSessions.add(session);
            }
            for (Session session : completedSessions) {
                sessionHistoryMap.remove(session.getSessionId());
                sessionHistoryList.remove(session);
            }
        }
    }

Please .. ;)