':return:
None or a unicode string of the distribution point\'s URL'

@property
def url(self):

    if (self._url is False):
        self._url = None
        name = self[u'distribution_point']
        if (name.name != u'full_name'):
            raise ValueError(unwrap(u'\n                                                                                CRL    distribution    points    that    are    relative    to    the    issuer    are\n                                                                                not    supported\n                                                                                '))
        for general_name in name.chosen:
            if (general_name.name == u'uniform_resource_identifier'):
                url = general_name.native
                if (url[0:7] == u'http://'):
                    self._url = url
                    break
    return self._url
