what does `return_uuids` mean in Weaviate retriever

[baixianger]

https://github.com/langchain-ai/chat-langchain/blob/2c63f20bdd278b40b44c3d127fe149538e67c9d9/backend/retrieval.py#L27-L46

As referenced here, I tried to change the vector db provider from Weaviate to Chroma. But i found the return_uuids will report an error

Why it works for Weaviate, but Chrome.

search_kwargs = {**configuration.search_kwargs, "return_uuids": True}
retriever = store.as_retriever(search_kwargs=search_kwargs)

I couldn't find any clue in the document about this parameter in both Weaviate and Chroma from langchain. Could anyone explain this to me?