filter_string += ',nsr-id-ref={}'.format(ns_instance['_id'])
else:
filter_string = '?nsr-id-ref={}'.format(ns_instance['_id'])
filter_string += ',nsr-id-ref={}'.format(ns_instance['_id'])
else:
filter_string = '?nsr-id-ref={}'.format(ns_instance['_id'])