code: @Override
    public BulkFuture<Map<String, Object>> asyncGetBulk(Collection<String> keys) {
      return asyncGetBulk(keys, transcoder);
    }
docs: Asynchronously get a bunch of objects from the cache and decode them with
  the given transcoder.
  
  @param keys the keys to request
  @return a Future result of that fetch
  @throws IllegalStateException in the rare circumstance where queue is too
  full to accept any more requests