GetValueOrDefault

public static TValue GetValueOrDefault<TKey, TValue>(this Dictionary<TKey, TValue> dic, TKey key, TValue defaultVal = default(TValue))
{
    TValue ret;
    return dic.TryGetValue(key, out ret) ? ret : defaultVal;
}

public static TValue GetValueOrDefault<TValue>(this StateBag stateBag, string key, TValue defaultValue = default(TValue))
{
    object value = stateBag[key];
    return Equals(value, null) ? defaultValue : (TValue) value;
}

public static T GetValueOrDefault<T>(this NameValueCollection coll, string key, T defaultValue = default(T))
{
    var value = coll.Get(key);
    return value == null ? defaultValue : ChangeType<T>(value);
}

public static string ChangeType(string value)
{
    return value;
}

public static T ChangeType<T>(string value)
{
    if (String.IsNullOrEmpty(value))
        return default(T);

    Type type = typeof(T);
    Type desiredType = Nullable.GetUnderlyingType(type) ?? type;

    if (desiredType.IsEnum) return (T)Enum.Parse(desiredType, value, true);
    return (T)Convert.ChangeType(value, desiredType);
}