docs: protected void onSessionClose(SessionImpl session) {
          Lock lock = lockManager.getLock(getLockingKey(session.keyspace()));
          lock.lock();
          try {
              if (keyspaceCacheMap.containsKey(session.keyspace())) {
                  KeyspaceCacheContainer cacheContainer = keyspaceCacheMap.get(session.keyspace());
                  cacheContainer.removeSessionReference(session);
                  // If there are no more sessions associated to current keyspace,
                  // close graph and remove reference from cache.
                  if (cacheContainer.referenceCount() == 0) {
                      JanusGraph graph = cacheContainer.graph();
                      graph.close();
                      keyspaceCacheMap.remove(session.keyspace());
                  }
              }
          } finally {
              lock.unlock();
          }
      }