Yes, Maxwell. I guess the docs are misleading, the code locate in https://github.com/python/cpython/blob/master/Objects/weakrefobject.c#L748

if (callback == Py_None)
        callback = NULL;
    if (callback == NULL)
        /* return existing weak reference if it exists */
        result = ref;
    if (result != NULL)
        Py_INCREF(result);
    else {
        ...
    }

However, I'm not sure we should fix the docs or the code here.