public static class IEnumerableExtensions {
    public static T MinBy<T, K>(this IEnumerable<T> source, Func<T, K> selector) {
        T min = default;

        bool anyValue = false;

        foreach (var item in source) {
            if (!anyValue || Comparer<K>.Default.Compare(selector(item), selector(min)) < 0) {
                min = item;
                anyValue = true;
            }
        }

        return min;
    }
}