exists before adding documents to it. Defaults to True.
            Additionally you can either pass in a client or an API key
            - client (PreviewVectorIndexClient): The Momento Vector Index client to use.
            - api_key (Optional[str]): The configuration to use to initialize
                the Vector Index with. Defaults to None. If None, the configuration
                is initialized from the environment variable `MOMENTO_API_KEY`.
        Returns:
            VST: Momento Vector Index vector store initialized from texts and
                embeddings.
        """
        from momento import (
            CredentialProvider,
            PreviewVectorIndexClient,
            VectorIndexConfigurations,
        )
        if "client" in kwargs:
            client = kwargs.pop("client")
        else:
            supplied_api_key = kwargs.pop("api_key", None)
            api_key = supplied_api_key or get_from_env("api_key", "MOMENTO_API_KEY")
            client = PreviewVectorIndexClient(
                configuration=VectorIndexConfigurations.Default.latest(),
                credential_provider=CredentialProvider.from_string(api_key),
            )
        vector_db = cls(embedding=embedding, client=client, **kwargs)  # type: ignore
        vector_db.add_texts(texts=texts, metadatas=metadatas, **kwargs)
        return vector_db