WeakRef has no constructor with argument

WeakRef cannot be used because it has neither constructor with arguments nor setters.

```
class WeakRef : public Reference {
public:

    static inline char *__get_class_name() { return (char *) "WeakRef"; }

    // enums

    // constants
    static void *operator new(size_t);
    static void operator delete(void *);

    // methods
    Variant get_ref() const;
};
```