          Creates a default instance of a flat relational field.
          """
          # TODO: filter queryset using:
          # .using(db).complex_filter(self.rel.limit_choices_to)
          kwargs = {
              'required': required,
              'queryset': model_class._default_manager,
              'many': to_many
          }
  
 
</s> remove             'required': not(model_field.null or model_field.blank),
            'queryset': model_field.rel.to._default_manager,
 </s> add             'required': required,
            'queryset': model_class._default_manager, </s> remove     def get_related_field(self, model_field, to_many=False):
 </s> add     def get_related_field(self, model_field, rel=None, to_many=False): </s> remove                 model = model_field.rel.to
 </s> add                 model = model_class </s> remove         return None
 </s> add         if self.opts.fields and model_field.name in self.opts.fields:
            return self.get_field(model_field) </s> remove     def get_nested_field(self, model_field):
 </s> add     def get_nested_field(self, model_field, rel=None):
        if rel:
            model_class = rel.model
            required = True
        else:
            model_class = model_field.rel.to
            required = not(model_field.null or model_field.blank)

          Creates a default instance of a flat relational field.
          """
          # TODO: filter queryset using:
          # .using(db).complex_filter(self.rel.limit_choices_to)
        if rel:
            model_class = rel.model
            required = True
        else:
            model_class = model_field.rel.to
            required = not(model_field.null or model_field.blank)

          kwargs = {
              'required': required,
              'queryset': model_class._default_manager,
              'many': to_many
          }
  
keep keep keep add keep keep keep keep keep keep
 First pass on automatically including reverse relationship 
rest_framework/serializers.py