diff --git a/docs/api-guide/filtering.md b/docs/api-guide/filtering.md
index 8e3bd9ef5..90cb2ce5a 100644
--- a/docs/api-guide/filtering.md
+++ b/docs/api-guide/filtering.md
@@ -75,7 +75,7 @@ We can override `.get_queryset()` to deal with URLs such as `http://example.com/
             by filtering against a `username` query parameter in the URL.
             """
             queryset = Purchase.objects.all()
-            username = self.request.query_params.get('username', None)
+            username = self.request.query_params.get('username')
             if username is not None:
                 queryset = queryset.filter(purchaser__username=username)
             return queryset
@@ -365,4 +365,4 @@ The [djangorestframework-word-filter][django-rest-framework-word-search-filter]
 [django-url-filter]: https://github.com/miki725/django-url-filter
 [drf-url-filter]: https://github.com/manjitkumar/drf-url-filters
 [HStoreField]: https://docs.djangoproject.com/en/3.0/ref/contrib/postgres/fields/#hstorefield
-[JSONField]: https://docs.djangoproject.com/en/3.0/ref/contrib/postgres/fields/#jsonfield
\ No newline at end of file
+[JSONField]: https://docs.djangoproject.com/en/3.0/ref/contrib/postgres/fields/#jsonfield