### What problem does this PR solve?
fix api reference empty bug
```
for chunk_i in answer['reference'].get('chunks',[]):
^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'list' object has no attribute 'get'
```
```
return np.array([d["relevance_score"] for d in res["results"]]), res["meta"]["tokens"]["input_tokens"]+res["meta"]["tokens"]["output_tokens"]
~~~^^^^^^^^^^^
KeyError: 'results'
```
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
32d5885b68