code: public static boolean canUseAsDelayedQueue(final Jedis jedis, final String key) {
          final String type = jedis.type(key);
          return (ZSET.equalsIgnoreCase(type) || NONE.equalsIgnoreCase(type));
      }
docs: Determines if the queue identified by the given key can be used as a delayed queue.
  
  @param jedis
  connection to Redis
  @param key
  the key that identifies a queue
  @return true if the key already is a delayed queue or is not currently used, false otherwise