Grabs the first URL out of a asn1crypto.x509.CRLDistributionPoints
        object

        :param distribution_points:
            The x509.CRLDistributionPoints object to pull the URL out of

        :return:
            A unicode string or None

def _get_crl_url(self, distribution_points):
        """
        Grabs the first URL out of a asn1crypto.x509.CRLDistributionPoints
        object

        :param distribution_points:
            The x509.CRLDistributionPoints object to pull the URL out of

        :return:
            A unicode string or None
        """

        if distribution_points is None:
            return None

        for distribution_point in distribution_points:
            name = distribution_point['distribution_point']
            if name.name == 'full_name' and name.chosen[0].name == 'uniform_resource_identifier':
                return name.chosen[0].chosen.native

        return None