Allow getter and on_change_with* to return Model instance
This will be some syntactic sugar which will simplify in some cases the code which need to test first if an attribute is filled before returning its id.
E.g:
def getter(self, name):
return self.parent.currency
instead of
def getter(self, name):
if self.parent.currency:
return self.parent.currency.id
But we must always convert the returned instance into id because we can not rely on the context of it.