code: def get_cgi_parameter_file(form: cgi.FieldStorage,
                             key: str) -> Optional[bytes]:
      
      (filename, filecontents) = get_cgi_parameter_filename_and_file(form, key)
      return filecontents
docs: Extracts a file's contents from a "file" input in a CGI form, or None
      if no such file was uploaded.