code: def make_good_url(url=None, addition="/"):
      
  
      if url is None:
          return None
  
      if isinstance(url, str) and isinstance(addition, str):
          return "%s/%s" % (url.rstrip('/'), addition.lstrip('/'))
      else:
          return None
docs: Appends addition to url, ensuring the right number of slashes
      exist and the path doesn't get clobbered.
  
      >>> make_good_url('http://www.server.com/anywhere', 'else')
      'http://www.server.com/anywhere/else'
      >>> make_good_url('http://test.com/', '/somewhere/over/the/rainbow/')
      'http://test.com/somewhere/over/the/rainbow/'
      >>> make_good_url('None')
      'None/'
      >>> make_good_url()
      >>> make_good_url({})
      >>> make_good_url(addition='{}')
  
      :param url: URL
      :param addition: Something to add to the URL
      :return: New URL with addition