code: def _merge(options, name, bases, default=None):
      
      result = None
      for base in bases:
          if base is None:
              continue
  
          value = getattr(base, name, None)
          if value is None:
              continue
  
          result = utils.cons(result, value)
  
      value = options.get(name)
      if value is not None:
          result = utils.cons(result, value)
  
      return result or default
docs: Merges a named option collection.