CompositionField seems to be hooking to every model when upgrading to Django 1.4

[catalanojuan]

We've been using django-composition with Django 1.3.5 for a while now, with no problems. Recently we started the process of upgrading to Django 1.4.3 and the code breaks when saving any database object. Here's the exception's trace. Note: the Activity model doesn't have a Composition field.

It seems that the CompositionField's handler we're using is being called for every save execution (of every model in our codebase) and not only for the model's to which we explicitly added a CompositionField. So it breaks when the handler tries to access data that's specific of only some of the models (the ones to which we actually added a CompositionField to).