          kwargs = get_url_kwargs(model)
  
          return field_cls, kwargs
  
      def build_unknown_field(self, field_name, info, model):
          """
          Raise an error on any unknown fields.
          """
          raise ImproperlyConfigured(
              'Field name `%s` is not valid for model `%s`.' %
 
</s> remove         relation_info = info.relations[field_name]

        field_cls = self.serializer_related_class
        kwargs = get_relation_kwargs(field_name, relation_info)
 </s> add         field_class = self.serializer_related_class
        field_kwargs = get_relation_kwargs(field_name, relation_info) </s> remove         return field_cls, kwargs
 </s> add         return field_class, field_kwargs </s> remove         if not issubclass(field_cls, HyperlinkedRelatedField):
            kwargs.pop('view_name', None)
 </s> add         if not issubclass(field_class, HyperlinkedRelatedField):
            field_kwargs.pop('view_name', None) </s> remove         return field_cls, kwargs
 </s> add         return field_class, field_kwargs </s> remove         field_cls = NestedSerializer
        kwargs = get_nested_relation_kwargs(relation_info)
 </s> add         field_class = NestedSerializer
        field_kwargs = get_nested_relation_kwargs(relation_info)
    def build_unknown_field(self, field_name, model_class):
          kwargs = get_url_kwargs(model)
  
          return field_cls, kwargs
  
    def build_unknown_field(self, field_name, model_class):
          """
          Raise an error on any unknown fields.
          """
          raise ImproperlyConfigured(
              'Field name `%s` is not valid for model `%s`.' %
keep keep keep keep replace keep keep keep keep keep
 Final bits of docs for ModelSerializer fields API 
rest_framework/serializers.py