diff --git a/sms4j-provider/src/main/java/org/dromara/sms4j/mas/utils/MasUtils.java b/sms4j-provider/src/main/java/org/dromara/sms4j/mas/utils/MasUtils.java
index 7c64e78d..f3e7be43 100644
--- a/sms4j-provider/src/main/java/org/dromara/sms4j/mas/utils/MasUtils.java
+++ b/sms4j-provider/src/main/java/org/dromara/sms4j/mas/utils/MasUtils.java
@@ -65,6 +65,8 @@ public class MasUtils {
         if (StrUtil.isNotEmpty(config.getAddSerial())){
             map.put("addSerial", config.getAddSerial().trim());
             sb.append(config.getAddSerial().trim());
+        }else {
+            map.put("addSerial", "");
         }
 
         map.put("mac", DigestUtil.md5Hex(sb.toString(), StandardCharsets.UTF_8));