      def get_pk_field(self, model_field):
          if self.opts.fields and model_field.name in self.opts.fields:
              return self.get_field(model_field)
  
      def get_related_field(self, model_field, related_model, to_many, has_through_model):
          """
          Creates a default instance of a flat relational field.
          """
          kwargs = {
              'queryset': related_model._default_manager,
 
</s> remove     def get_pk_field(self, model_field):
 </s> add     def get_pk_field(self, field_name, model_field): </s> remove         return self.get_field(model_field)
 </s> add         return self.get_field(field_name, model_field) </s> remove     def get_related_field(self, model_field, related_model, to_many, has_through_model):
 </s> add     def get_related_field(self, field_name, model_field, related_model, to_many, has_through_model): </s> remove     def get_nested_field(self, model_field, related_model, to_many, has_through_model):
 </s> add     def get_nested_field(self, field_name, model_field, related_model, to_many, has_through_model): </s> remove     def get_pk_field(self, model_field):
 </s> add     def get_pk_field(self, field_name, model_field):
    def get_related_field(self, field_name, model_field, related_model, to_many, has_through_model):
      def get_pk_field(self, model_field):
          if self.opts.fields and model_field.name in self.opts.fields:
              return self.get_field(model_field)
  
    def get_related_field(self, field_name, model_field, related_model, to_many, has_through_model):
          """
          Creates a default instance of a flat relational field.
          """
          kwargs = {
              'queryset': related_model._default_manager,
keep keep keep keep replace keep keep keep keep keep
 Drop label from serializer fields when not needed 
rest_framework/serializers.py