code: public Set<HK> keys(H key, HK field) {
          final byte[] rawKey = rawKey(key);
          final byte[] rawHashKey = rawHashKey(field);
  
          Set<byte[]> rawElementNames = execute(new RedisCallback<Set<byte[]>>() {
              public Set<byte[]> doInRedis(RedisConnection connection) throws DataAccessException {
                  return ((RedisClusterConnection) connection).slKeys(rawKey, rawHashKey);
              }
          }, true);
  
          return deserializeHashKeys(rawElementNames);
      }
docs: /*
  @see SessionOfHashListOperations#keys(java.lang.Object, java.lang.Object)