Force-evaluate querysets (see #2602)

rest_framework/serializers.py

@@ -562,7 +562,7 @@ def to_representation(self, data):
         """
         # Dealing with nested relationships, data can be a Manager,
         # so, first get a queryset from the Manager if needed
-        iterable = data.all() if isinstance(data, models.Manager) else data
+        iterable = data.all() if isinstance(data, (models.Manager, models.QuerySet)) else data
         return [
             self.child.to_representation(item) for item in iterable
         ]