Llama-index how to execute search query against OpenSearch Elasticsearch index?

I have this code where I am able to create an index in Opensearch Elasticsearch:

def openes_initiate(file):    endpoint = getenv("OPENSEARCH_ENDPOINT", "http://localhost:9200")    # index to demonstrate the VectorStore impl    idx = getenv("OPENSEARCH_INDEX", "llama-osindex-demo")    UnstructuredReader = download_loader("UnstructuredReader")    loader = UnstructuredReader()    documents = loader.load_data(file=Path(file))    # OpensearchVectorClient stores text in this field by default    text_field = "content"    # OpensearchVectorClient stores embeddings in this field by default    embedding_field = "embedding"    # OpensearchVectorClient encapsulates logic for a    # single opensearch index with vector search enabled    client = OpensearchVectorClient(endpoint, idx, 1536, embedding_field=embedding_field, text_field=text_field)    # initialize vector store    vector_store = OpensearchVectorStore(client)    storage_context = StorageContext.from_defaults(vector_store=vector_store)    # initialize an index using our sample data and the client we just created    index = GPTVectorStoreIndex.from_documents(documents=documents,storage_context=storage_context)

Issue I am having is that once I have indexed the data, I am unable to reload it and serve a query against it. I tried to do this:

def query(index,question):    query_engine = index.as_query_engine()    res = query_engine.query(question)    print(res.response)

Where index is the one I created in first piece of code, but it returns None