Rudder

A rule can refer non existing item (missing directive or group). It should only happens when something VERY wrong happened, and so, in that case, we try hard to make the information really apparent to the user (with a big red error line in the grid of rule).

We also try to disable the corresponding rule, because chance are hight that the rule won't be doing what you want in that case.

But for that, we don't use the currently saved rule, only the copy available in the page displaying at the moment - and the two may have differ. So we can commit other modification than just disabling the rule!