优化mqlinster代码结构，减少重复代码

 package com.yoho.search.consumer.index.increment.productIndex;
 
 import com.alibaba.fastjson.JSONArray;
+import com.alibaba.fastjson.JSONObject;
 import com.rabbitmq.client.Channel;
 import com.yoho.error.event.SearchEvent;
 import com.yoho.search.base.utils.ConvertUtils;
@@ -92,7 +93,8 @@ public class ActivityProductMqListener extends AbstractMqListener implements Cha
         Map<String, Object> indexData = new HashMap<>();
         indexData.put("productId", productId);
         if (CollectionUtils.isEmpty(activityProducts)) {
-            indexData.put("activities", "");
+            jsonArray.add(new JSONObject());
+            indexData.put("activities", jsonArray);
         }else{
             for (ActivityProduct activityProduct : activityProducts) {
                 jsonArray.add(activityProductService.getActivities(activityProduct));