In general, when you see a feature like `attached_timer' in our code, this was an addition from the early stage of conversion to void-safety when we did not know better. Such routines should be removed and everywhere `timer' is used, we should simply check that it is set via an object test.
Now in this particular case, there is no need to set `timer' to Void, we just need to make sure it is not going to be triggered again. And thus we can make it attached and remove the `attached_timer' query.