@Override
    public Collection<V> values()
    {
        return Collections.unmodifiableCollection( cache.asMap().values() );
    }
<strong>IMPORTANT:</strong> Unlike the standard {@link Map#values()} implementation, the collection returned from
this method cannot be modified.

@return an unmodifiable collection view of the values contained in this map
xmppserver/src/main/java/org/jivesoftware/util/cache/CaffeineCache.java