C# List.Sort 方法可能自己比较自己

最近代码突然报错
如下:

  pps = pps.Sort((t0, t1) =>
            {                
                var c = t0.Variety.DeliveryYearMonth.CompareTo(t1.Variety.DeliveryYearMonth);
                if (c != 0)
                    return c;
                c = (t0.Variety.IsCall ? 1 : -1) * (t1.Variety.IsCall ? 1 : -1);
                if (c != 1)
                    return t0.Variety.IsCall ? -1 : 1;
                c = (t0.Variety.GetStrike(_tday).CompareTo(t1.Variety.GetStrike(_tday)));
                if (c != 0)
                    return c;
                c = (t0.Variety.GetContractMultiplier(_tday).CompareTo(t1.Variety.GetContractMultiplier(_tday)));
                if (c != 0)
                    return c;
                throw new NotSupportedException();          
            });

因为集合 pps 中的Variety对象不会有重复的，所以在Sort中遇到两个完全相同的对象，我就认为之前比较的代码出了逻辑错误。
随后升级到4.7之后，这里就会遇到异常，Sort 在比较两个完全一样的对象，就是自己比较自己，查阅了StackOverflow:

https://stackoverflow.com/questions/7373652/in-the-listt-sort-method-is-an-item-ever-compared-to-itself

This method uses Array.Sort, which uses the QuickSort algorithm.

QuickSort will never compare an item to itself. Some implementations of QuickSort compare items to themselves. This can also happen if that item occurs more than once in your List.

Either way, in order for your comparison function to be a proper, well-behaved comparison function, you need to handle the case of elements being compared to themselves.