input: Write a function to parse the given URL and print out the protocol, domain name, and path using Python. If the input URL is empty, return None.
  assert parse_url('https://www.example.com/path/to/file')=='Protocol: https\nDomain name: www.example.com\nPath: /path/to/file'
  assert parse_url('http://www.test.com/home')=='Protocol: http\nDomain name: www.test.com\nPath: /home'
  assert parse_url('ftp://files.domain.com/folder/file.txt')=='Protocol: ftp\nDomain name: files.domain.com\nPath: /folder/file.txt'
  assert parse_url('')==None
output: def parse_url(url):
      if not url:
          return None
      from urllib.parse import urlparse
      parsed_url = urlparse(url)
      protocol = parsed_url.scheme
      domain_name = parsed_url.netloc
      path = parsed_url.path
      return f'Protocol: {protocol}\nDomain name: {domain_name}\nPath: {path}'