fix #723 (#724)

diff --git a/dubbo-admin-ui/src/components/apiDocs/ApiFormItem.vue b/dubbo-admin-ui/src/components/apiDocs/ApiFormItem.vue
index 902a00e..5156039 100644
--- a/dubbo-admin-ui/src/components/apiDocs/ApiFormItem.vue
+++ b/dubbo-admin-ui/src/components/apiDocs/ApiFormItem.vue
@@ -220,7 +220,7 @@
         var defaultValue = this.formItemInfo.get('defaultValue')
         if (defaultValue) {
           this.selectDefaultValue = defaultValue
-          this.formValues.set(this.buildItemId(), defaultValue[0])
+          this.formValues.set(this.buildItemId(), defaultValue)
         } else {
           this.formValues.set(this.buildItemId(), '')
         }