docs: public void addConnection(RedisURI redisURI, StatefulRedisConnection<String, String> connection) {
  
          if (this.closed) { // fastpath
              connection.closeAsync();
              return;
          }
  
          synchronized (this.connections) {
  
              if (this.closed) {
                  connection.closeAsync();
                  return;
              }
  
              this.connections.put(redisURI, connection);
          }
      }