Messages are being stored in Firestore as string

I followed [this doc ](https://python.langchain.com/docs/integrations/memory/google_firestore/#cleaning-up)to incorporate Firestore chat message history into my app. Everything is working fine, EXCEPT that the message history JSON objects are stored in Firestore as strings rather than JSON.

#### Environment details

langchain-google-firestore = "^0.3.0"

Here is the screenshot of how it looks in the Firestore console:


My suspicion is this line is not working as expected, although it should - https://github.com/googleapis/langchain-google-firestore-python/blob/79c19379985f7474b92766ee7f22386e772c2747/src/langchain_google_firestore/chat_message_history.py#L75

I could be wrong. Would really appreciate any workaround.