Get an ACL by ID belonging to the instance specified by name.

        :param str instance: The name of the instance from which to fetch the ACL.
        :param str acl: The ID of the ACL to fetch.
        :returns: An :py:class:`Acl` object, or None if ACL does not exist.
        :rtype: :py:class:`Acl`

def get(self, instance, acl):
        """Get an ACL by ID belonging to the instance specified by name.

        :param str instance: The name of the instance from which to fetch the ACL.
        :param str acl: The ID of the ACL to fetch.
        :returns: An :py:class:`Acl` object, or None if ACL does not exist.
        :rtype: :py:class:`Acl`
        """
        base_url = self._url.format(instance=instance)
        url = '{base}{aclid}/'.format(base=base_url, aclid=acl)
        response = requests.get(url, **self._default_request_kwargs)
        data = self._get_response_data(response)
        return self._concrete_acl(data)