上传组件兼容element-plus最新版本

src/components/FileUpload/index.vue

@@ -170,7 +170,9 @@ function listToString(list, separator) {
   let strs = "";
   separator = separator || ",";
   for (let i in list) {
-    strs += list[i].url + separator;
+    if(undefined !== list[i].url) {
+      strs += list[i].url + separator;
+    }
   }
   return strs != '' ? strs.substr(0, strs.length - 1) : '';
 }