delegate !is null

[Saaa]

Hope this one makes any sense :)

C c = new C;
C mouseOverObject = c;

int delegate() deleg = &mouseOverObject.getSomeVariable;
mouseOverObject = null;

int value;
void write()
{
if(deleg !is null) //how do I make this check for (mouseOverObject !is 
null)?
{
value = deleg();
}
writefln( value);
}

mainloop:
... code which may change mouseOverObject to be null or any C object
write();
goto mainloop;