code: func (t *CarouselTemplate) MarshalJSON() ([]byte, error) {
  	return json.Marshal(&struct {
  		Type             TemplateType         `json:"type"`
  		Columns          []*CarouselColumn    `json:"columns"`
  		ImageAspectRatio ImageAspectRatioType `json:"imageAspectRatio,omitempty"`
  		ImageSize        ImageSizeType        `json:"imageSize,omitempty"`
  	}{
  		Type:             TemplateTypeCarousel,
  		Columns:          t.Columns,
  		ImageAspectRatio: t.ImageAspectRatio,
  		ImageSize:        t.ImageSize,
  	})
  }
docs: // MarshalJSON method of CarouselTemplate