input: Write a function to parse a given URL and print out its protocol, domain name, and path using Python. If the URL is empty, return None.
  
  assert url_parser('https://www.example.com/path/to/file') == ('https', 'www.example.com', '/path/to/file')
  assert url_parser('http://test.com/some/path') == ('http', 'test.com', '/some/path')
  assert url_parser('') == None
output: def url_parser(url):
      if not url:
          return None
      parsed_url = urlparse(url)
      return (parsed_url.scheme, parsed_url.netloc, parsed_url.path)