refine templates of graph (#1368)

### What problem does this PR solve?

#918 
### Type of change

- [x] New Feature (non-breaking change which adds functionality)

graph/test/dsl_examples/headhunter_zh.json

@@ -205,6 +205,6 @@
   "history": [],
   "messages": [],
   "path": [],
-  "reference": {},
+  "reference": [],
   "answer": []
 }