code: @Override
    public Collection<String> getCacheNames() {
      Set<String> cacheNames = new HashSet<>();
      for (org.cache2k.Cache<?,?> cache : manager.getActiveCaches()) {
        cacheNames.add(cache.getName());
      }
      cacheNames.addAll(configuredCacheNames);
      return Collections.unmodifiableSet(cacheNames);
    }
docs: Get a list of known caches. Depending on the configuration, caches may be created
  dynamically without providing a configuration for a specific cache name. Because of this
  combine the known names from configuration and activated caches.