// t(o.Ot)

gistfile1.txt

    public static class DictionaryExtensions
    {
        public static TValue GetValueOrDefault<TKey, TValue>(this IDictionary<TKey, TValue> dictionary, TKey key)
        {
            return dictionary.GetValueOrDefault(key, x=>default(TValue));
        }

        public static TValue GetValueOrDefault<TKey, TValue>(this IDictionary<TKey, TValue> dictionary, TKey key,
            Func<TKey, TValue> func)
        {
            TValue result;
            return dictionary.TryGetValue(key, out result) ? result : func(key);
        }

        public static TValue GetValueOrDefault<TKey, TValue>(this IDictionary<TKey, TValue> dictionary, TKey key, TValue value)
        {
            TValue result;
            return dictionary.TryGetValue(key, out result) ? result : value;
        }
    }

http://stackoverflow.com/questions/2601477/dictionary-returning-a-default-value-if-the-key-does-not-exist