          self.assertTrue(serializer.is_valid())
          self.assertEquals(serializer.data, data)
          serializer.save()
  
          # # Ensure source 1 is updated, and everything else is as expected
          queryset = ForeignKeySource.objects.all()
          serializer = ForeignKeySourceSerializer(queryset)
          expected = [
              {'id': 1, 'name': u'source-1', 'target': 2},
              {'id': 2, 'name': u'source-2', 'target': 1},
 
</s> remove         into[(self.source or field_name)] = self.from_native(value)
 </s> add         if value is None and not self.blank:
            raise ValidationError('Value may not be null')
        elif value is None and self.blank:
            into[(self.source or field_name)] = None
        else:
            into[(self.source or field_name)] = self.from_native(value) </s> remove         queryset = rel._default_manager
 </s> add  </s> remove             return ManyPrimaryKeyRelatedField(queryset=queryset)
        return PrimaryKeyRelatedField(queryset=queryset)
 </s> add             return ManyPrimaryKeyRelatedField(**kwargs)
        return PrimaryKeyRelatedField(**kwargs) </s> remove         response = self.detail_view(request, pk=1).render()
 </s> add         response = self.detail_view(request, pk=1)
        # Ensure source 1 is updated, and everything else is as expected
          self.assertTrue(serializer.is_valid())
          self.assertEquals(serializer.data, data)
          serializer.save()
  
        # Ensure source 1 is updated, and everything else is as expected
          queryset = ForeignKeySource.objects.all()
          serializer = ForeignKeySourceSerializer(queryset)
          expected = [
              {'id': 1, 'name': u'source-1', 'target': 2},
              {'id': 2, 'name': u'source-2', 'target': 1},
keep keep keep keep replace keep keep keep keep keep
 Support nullable FKs, with blank=True 
rest_framework/tests/pk_relations.py