C# sort System.InvalidOperationException: Failed to compare two elements in the ar

System.InvalidOperationException: Failed to compare two elements in the array. ---> System.NullReferenceException: Object reference not set to an instance of an object.

第一次用C#sort遇到的，感觉和它的底层实现有关。

抛异常的写法：
List<GuildBattleFieldRank> redList = new List<GuildBattleFieldRank>();
redList.Sort((l, r) =>
            {
                if (l.Score >= r.Score)
                    return -;
                return ;
            });

解决方法：
List<GuildBattleFieldRank> redList = new List<GuildBattleFieldRank>();
redList.Sort((l, r) =>
            {
                if (l.Score == r.Score) return ;
                else if (l.Score > r.Score)
                    return -;
                return ;
            });