4、使用可空类型 static double? GetNul lab leDouble o double? result. string user Input ReadLine o try result double Parse(user Input) catch resu nu return result static Vector GetVector(str ing name Write ine($"请输入矢量{name}的大小值:"); double? r =GetNul lableDouble o Wr iteL ine($"请输入矢量{name}的角度值:") double? theta =GetNul l ableDouble o return new Vector(r, theta4、使用可空类型