input: Write a function to parse the given URL and print out the protocol, domain name, and path using Python. The function should return the protocol, domain name, and path as a tuple, in order. If the URL is empty, the function should return None.
  assert parse_url('https://www.example.com/path/to/file')==('https', 'www.example.com', '/path/to/file')
  assert parse_url('http://example.org/some/path')==('http', 'example.org', '/some/path')
  assert parse_url('ftp://user:password@ftp.example.com/')==('ftp', 'user:password@ftp.example.com', '/')
  assert parse_url('')==None
output: def parse_url(url):
      if not url:
          return None
      protocol = url.split('://')[0]
      remaining = url.split('://')[1]
      domain = remaining.split('/')[0]
      path = '/' + '/'.join(remaining.split('/')[1:])
      return (protocol, domain, path)