Merge pull request #4097 from django-oscar/fix_makemigrations_issues

Add default auto field for django 3

sandbox/settings.py

@@ -325,6 +325,8 @@ AUTH_PASSWORD_VALIDATORS = [
     },
 ]
 
+DEFAULT_AUTO_FIELD = 'django.db.models.AutoField'
+
 LOGIN_REDIRECT_URL = '/'
 APPEND_SLASH = True