langchain/chat_models/openai.py/_convert_dict_to_message
def _convert_dict_to_message(_dict: dict) -> BaseMessage:
    role = _dict["role"]
    if role == "user":
        return HumanMessage(content=_dict["content"])
    elif role == "assistant":
        return AIMessage(content=_dict["content"])
    elif role == "system":
        return SystemMessage(content=_dict["content"])
    else:
        return ChatMessage(content=_dict["content"], role=role)