Gets vfg node at @addr
        Returns VFGNode or None

def _vfg_node(self, addr):
        """
        Gets vfg node at @addr
        Returns VFGNode or None
        """
        for n in self._vfg._nodes.values():
            if n.addr == addr:
                return n
        raise DataGraphError("No VFG node at 0x%x" % addr)