docs: public void sessionRemoved(final MemcachedBackupSession session) {
          if(!_sticky) {
              if(session.isLocked()) {
                  _lockingStrategy.releaseLock(session.getIdInternal());
                  session.releaseLock();
              }
              _invalidSessionsCache.put(session.getIdInternal(), Boolean.TRUE);
          }
      }