How to check a "NULL object reference" in Managed C++?

I come across some MC++ code like this:

__gc class ClassA
{
Puclic:
     ClassB GetClassB();
}

__gc class ClassB
{
 Public:
    int Value;
}

int main()
{
    ClassA^ a = gcnew ClassA();
    ClassB^ b = a->GetClassB();

    int c = b->Value;
}

Isn't it important to check whether b is NULL before access to its value? I tried if(b == NULL), but it dosen't work.

Or it's really not necessary to do the check? however I can hardly believe it...

PS: I only want to know whether the "Reference" itself could be NULL here. Whether the content of class B is null isn't important.