code: public CacheKeyBuilder appendCacheables(Collection<? extends Cacheable> input)
    {
      appendItem(CACHEABLE_LIST_KEY, cacheableCollectionToByteArray(input, true));
      return this;
    }
docs: Add a collection of Cacheables to the cache key.
  Cacheables in the collection are concatenated without any separator,
  and they appear in the cache key in their input order.
  
  @param input a collection of Cacheables to be included in the cache key
  @return this instance