boost::unsafe_any_cast invalid non-null pointer when empty?

I've got a piece of code in which I use boost::unsafe_any_cast<void*>(&boost::any anyInstance) to obtain the content pointer of a boost::any object. The code is this below:

boost::any staticResult;  //contains a private pointer called content
f(staticResult);          //makes the content pointer a null pointer 
void* voidStaticResult = boost::unsafe_any_cast<void*>(&staticResult);

Unfortunately, debugging, I see that the content pointer in staticResult is NULL (0x00000000) while voidStaticResult is 0x00000004.

(Apparently there's no reason for that. Have you got any ideas?)

EDIT: The function f() calls a dll creating an instance of an object. The instance is pointed by the content pointer of staticResult. I need to pass the pointer to another function, but it seems to me there's no easy way to "cast" boost::any to a pointer to the instantiated class. Any other solution would be great.

Probably unsafe any cast is only valid for non empty any's. It is unsafe and unchecked.

Any is often implemented as a pointer at a block of memory where there is a vtable followed by the object instance. So to get a pointer to the object, you add sizeof(vtable ptr) to the any internal pointer, 4 on your build.