code: def url(self):
          
  
          if self._url is False:
              self._url = None
              name = self['distribution_point']
              if name.name != 'full_name':
                  raise ValueError(unwrap(
                      '''
                      CRL distribution points that are relative to the issuer are
                      not supported
                      '''
                  ))
  
              for general_name in name.chosen:
                  if general_name.name == 'uniform_resource_identifier':
                      url = general_name.native
                      if url.lower().startswith(('http://', 'https://', 'ldap://', 'ldaps://')):
                          self._url = url
                          break
  
          return self._url
docs: :return:
              None or a unicode string of the distribution point's URL