No async_client for VertexAILLM

[xpilasneo4j]

Writing some code for various LLMs, it works with AzureOpenAI and OpenAI but not with VertexAI
Here is my code

    res_pipeline = await define_and_run_pipeline(llm, file_path)
    await llm.async_client.close()
    return res_pipeline

and here is the error

 File "C:\Users\XavierPilas\Documents\GitHub\rag-graphrag\GenericGraphRag\loadDataFromPDF.py", line 167, in main
    await llm.async_client.close()
          ^^^^^^^^^^^^^^^^
AttributeError: 'VertexAILLM' object has no attribute 'async_client'