Make abstract class refactoring is not working

[cpt9m0]

Describe the bug The make_abstract_class refactoring existing in refactorings/make_abstract_class.py is not working at all!

To Reproduce Steps to reproduce the behavior:

1. Go to 'refactorings/make_abstract_class.py'
2. Run the script on your test project
3. See the problem

Expected behavior Makes a class abstract, and propagates changes