old_contents: def listify(obj):
      ''' Wraps all non-list or tuple objects in a list; provides a simple
      way to accept flexible arguments. '''
      if obj is None:
          return []
      else:
          return obj if isinstance(obj, (list, tuple, type(None))) else [obj]
  
  
  def transformer(func):
      ''' Decorator that indicates that a method acts as a data transformer. '''
      def wrapper(self, *args, **kwargs):
         self.transform(func.__name__, *args, **kwargs)
      return wrapper
new_contents: def listify(obj):
      ''' Wraps all non-list or tuple objects in a list; provides a simple
      way to accept flexible arguments. '''
      if obj is None:
          return []
      else:
          return obj if isinstance(obj, (list, tuple, type(None))) else [obj]
  
subject: drop transformation wrapper