mute_subscription is null in update_mute_after_subscription_change

[Gavin Panella]

In Chromium, on https://bugs.launchpad.net/launchpad/+bug/753249, I
clicked Subscribe, the spinner briefly shows, then the page returns to
its previous state. The console log shows:

{{{
Uncaught TypeError: Cannot call method 'get' of null
get_mute_subscription launchpad.js:457
on_success launchpad.js:480
b.Subscriber._notify launchpad.js:2
b.Subscriber.notify launchpad.js:2
b.CustomEvent._notify launchpad.js:2
b.CustomEvent._procSubs launchpad.js:2
b.CustomEvent.fireSimple launchpad.js:2
b.CustomEvent.fire launchpad.js:2
t launchpad.js:2
B launchpad.js:2
R launchpad.js:2
}}}

I am however able to subscribe at
https://bugs.launchpad.net/launchpad/+bug/753249/+subscribe and
unsubscribe in the bug page itself (i.e. with ajax).

I was able to reproduce this bug reliably, so, as most people will not
be aware of the workaround, I am marking it as Critical.

[Martin Stjernholm (msub)]

I'm experiencing a problem with the same effects for
https://bugs.launchpad.net/ubuntu/+bug/704105. I'm using Firefox 3.6, and get this in the Firebug console:

show_widget_node is null
  show_widget_node.set('innerHTML', 'Choose…');
704105 (line 552)

[Henning Eggers (henninge)]

This bug only happens when structural bug subscriptions are *not* enabled which is currently only the case on qastaging (for members of betatesters). The code has changed since this was reported but it now found in update_mute_after_subscription_change which is called even without the mute option being on the page. Also, this seems to not be critical anymore since it does not hinder the actual subscription.
Anyway, easy fix, I'll do it anyway.

[Launchpad QA Bot (lpqabot)]

Fixed in stable r13118 <http://bazaar.launchpad.net/~launchpad-pqm/launchpad/stable/revision/13118>.

[Launchpad QA Bot (lpqabot)]

Fixed in db-stable r10602 <http://bazaar.launchpad.net/~launchpad-pqm/launchpad/db-stable/revision/10602>.