C++/CX支持C#传递可空类型参数

public ref class Class1 sealed
    {
    public:
        Class1(){}
        Platform::IBox<int>^ Multiply(Platform::IBox<int>^ a, Platform::IBox<int>^ b)
        {
            if(a == nullptr || b == nullptr)
                return nullptr;
            else
                return ref new Platform::Box<int>(a->Value * b->Value);
        }
    };

Class1 obj = new BoxingDemo.Class1();
int? a = null;
int? b = 5;
var result = obj.Multiply(a,b); //result = null