I am trying to initialize vertexai llm in langchain library.

from langchain_community.llms.vertexai import VertexAI
    
llm = VertexAI(
        max_output_tokens=1024,
        temperature=0.2,
        top_p=0.8,
        top_k=40,
        verbose=True,
    )

I get the following error with this.

ConfigError: field “client” not yet prepared so the type is still a
ForwardRef, you might need to call VertexAI.update_forward_refs().

And when I called this function I got.

NameError: name ‘_LanguageModel’ is not defined

I also went through the source code and tried importing _LanguageModel manually just before the code but it’s not working.
How can I resolve this?