Hello, I have an issue when using

    index = VectorStoreIndex.from_vector_store(
                vector_store=vector_store,
                embed_model=embed_model
            )

    indexes.append(index.as_retriever(similarity_top_k=12))

retriever = QueryFusionRetriever(
    retrievers=indexes,
    llm=llm,
    mode=FUSION_MODES.SIMPLE,
    similarity_top_k=12,
    num_queries=1,
    use_async=False,
    verbose=True
)

query_engine = RetrieverQueryEngine.from_args(
            retriever,
            llm=llm,
            qa_prompt_template=qa_prompt_template,
            refine_prompt_template=refine_prompt_template,
        )


chat_engine = CondenseQuestionChatEngine.from_defaults(
            query_engine=query_engine,
            verbose=True,
        )
response = chat_engine.chat(question)

bm25_retriever = BM25Retriever.from_defaults(nodes=nodes, similarity_top_k=12)