If i edit a class using the typical url from before 3.9 and then change the attribute order eZ crashes due to a missing language parameter.

So, in the admin use the url '<admin>/class/edit/2'. Notice that the title and name of the class is missing here.

Now click on any up/down arrow for a class attribute to change its order and eZ will crash.

Its possible to get into this state if you view an object and choose to edit the class via the icon javascript popup for it - note this is not the left menu icon but the icon in the center of the screen.

So two things to do here.

1) Fix the class edit link from the object to include the language.
2) When editing make sure a default language is set for backwards compatibility...

updated by la:
3) Fix fatall error(see attached image).

Steps to reproduce

Use the url '<admin>/class/edit/2'.

Notice that the title and name of the class is missing here.

Now click on any up/down arrow for a class attribute to change its order and eZ will crash.