input: def read_url(url: str) -> str:
      """ Read the contents from a given URL.
      >>> read_url('https://www.example.com')
      '<!doctype html>\n<html>'  # Simplified for demonstration purposes
      >>> read_url('https://www.nonexistentwebsite.com')
      None
      """
output:     import requests
      try:
          response = requests.get(url)
          response.raise_for_status()
          return response.text
      except requests.RequestException:
          return None