How to get value of a key in redis cluster using redisson client

I am trying to get value of a key in redis cluster using redisson client .

Config config = new Config();        config.useClusterServers()          .addNodeAddress("redis://localhost:6380","redis://localhost:6379","redis://localhost:6381");        RedissonClient redisson = Redisson.create(config);        RMapCache<String, String> map = redisson.getMapCache("db0");        System.out.println("Key value  is :  "+map.get("key"));

I have got db0 as keyspace from this command result

INFO keyspace

db0:keys=1,expires=0,avg_ttl=0

but the result is :

Key value is : null