code: func (m *StickerMessage) MarshalJSON() ([]byte, error) {
  	return json.Marshal(&struct {
  		Type       MessageType      `json:"type"`
  		PackageID  string           `json:"packageId"`
  		StickerID  string           `json:"stickerId"`
  		QuickReply *QuickReplyItems `json:"quickReply,omitempty"`
  	}{
  		Type:       MessageTypeSticker,
  		PackageID:  m.PackageID,
  		StickerID:  m.StickerID,
  		QuickReply: m.quickReplyitems,
  	})
  }
docs: // MarshalJSON method of StickerMessage