如何表明方法不成功

I have several similar methods, say eg. CalculatePoint(...) and CalculateListOfPoints(...). Occasionally, they may not succeed, and need to indicate this to the caller. For CalculateListOfPoints, which returns a generic List, I could return an empty list and require the caller to check this; however Point is a value type and so I can't return null there.I have several similar methods, say eg. Calcula