docs: Collection<Tuple2<Long, Long>> getSessionsToExpire() {
          List<Tuple2<Long, Long>> expired = new ArrayList<Tuple2<Long, Long>>();
          long now = Clock.currentTimeMillis();
          for (CPSessionInfo session : sessions.values()) {
              if (session.isExpired(now)) {
                  expired.add(Tuple2.of(session.id(), session.version()));
              }
          }
  
          return expired;
      }