          """
          data = {'id': 1, 'name': u'source-1', 'target': ''}
          expected_data = {'id': 1, 'name': u'source-1', 'target': None}
          instance = NullableForeignKeySource.objects.get(pk=1)
          serializer = NullableSlugSourceSerializer(instance, data=data)
          self.assertTrue(serializer.is_valid())
          self.assertEquals(serializer.data, expected_data)
          serializer.save()
  
          # Ensure source 1 is updated, and everything else is as expected
 
</s> remove         serializer = NullableSlugSourceSerializer(instance, data=data)
 </s> add         serializer = NullableForeignKeySourceSerializer(instance, data=data) </s> remove         serializer = NullableSlugSourceSerializer(data=data)
 </s> add         serializer = NullableForeignKeySourceSerializer(data=data) </s> remove         serializer = NullableSlugSourceSerializer(queryset)
 </s> add         serializer = NullableForeignKeySourceSerializer(queryset) </s> remove         serializer = NullableSlugSourceSerializer(queryset)
 </s> add         serializer = NullableForeignKeySourceSerializer(queryset) </s> remove         serializer = NullableSlugSourceSerializer(queryset)
 </s> add         serializer = NullableForeignKeySourceSerializer(queryset)
        serializer = NullableForeignKeySourceSerializer(instance, data=data)
          """
          data = {'id': 1, 'name': u'source-1', 'target': ''}
          expected_data = {'id': 1, 'name': u'source-1', 'target': None}
          instance = NullableForeignKeySource.objects.get(pk=1)
        serializer = NullableForeignKeySourceSerializer(instance, data=data)
          self.assertTrue(serializer.is_valid())
          self.assertEquals(serializer.data, expected_data)
          serializer.save()
  
          # Ensure source 1 is updated, and everything else is as expected
keep keep keep keep replace keep keep keep keep keep
 Raise Validation Errors when relationships receive incorrect types. Fixes #590. 
rest_framework/tests/relations_slug.py