[BUG] Chunk Data Not Being Saved to S3 Bucket in v2.3.0

## 🐞Describe the bug

In version 2.3.0, chunk data is being registered as null. This issue did not occur in versions prior to v2.3.0.

## 🔄 To Reproduce

Steps to reproduce the behavior:

1.Use the application in version 2.3.0

## 📷 Screenshots

・Execute a SQL query in Athena to retrieve chatbot conversation data.

・Verify the S3 bucket contents and observe that the chunk data is registered as null.

　・Before v2.3.0:
　　- d.newimage.MessageMap.S
　　　used_chunks:[{"content":~~~~~}]
　・v2.3.0:
　　- d.newimage.MessageMap.S
　　　used_chunks: null

## 🔎 Logs for Chat Issues

## 🔎 Logs for Bot Creation/Update Issues

## 📝 Additional context

Chunk data is really helpful for making chatbot answers better. I'd love to see the ability to register chunk data in v2.3.0.

Start by reproducing the issue in version 2.3.0, then inspect the S3 record and the Athena query result for d.newimage.MessageMap.S. Compare the persisted used_chunks value with a version before v2.3.0. Done means chunk data is saved in S3 and used_chunks is no longer null.

Written by the indexing model from the issue text.