Extension method for ServiceStack ICacheClient that fetches an item from the cache or adds it if it is not there.

ICacheClientExtensions.cs

public static T GetOrAdd<T>(this ICacheClient cache, string key, DateTime expiresAt, Func<T> getItemToCacheDelegate)
{
    T item;
    var itemIsInCache = !cache.Add(key, "", expiresAt);

    if (itemIsInCache)
    {
        item = cache.Get<T>(key);
    }
    else
    {
        item = getItemToCacheDelegate();
        cache.Set(key, item, expiresAt);
    }

    return item;
}

I'm using the success or failure of the Add call to determine if the item is already in the cache. This is to account for value types. If I simply do a Get on the item and check for null I will get the wrong result for a value type that is not actually in the cache yet (default value). The downside of this implementation is the extra trip to the cache. Any ideas for improvement are welcome!