use of deprecated wagtail function

if isinstance(objs, collections.Iterable):
discuss_data/ddusers/tests/test_views.py::SearchResultsViewTests::test_search_last_name
  /usr/local/lib/python3.7/site-packages/wagtail/core/middleware.py:12: RemovedInWagtail211Warning: wagtail.core.middleware.SiteMiddleware and the use of request.site is deprecated. Please update your code to use Site.get_for_request(request) in place of request.site, and remove wagtail.core.middleware.SiteMiddleware from MIDDLEWARES
    RemovedInWagtail211Warning