def validate_api_key(api_key: str) -> None:
    """
    Validates the provided API key.

    Args:
        api_key (str): The API key to be validated.

    Raises:
        ValueError: If the API key is empty or None.

    Returns:
        None

    """
    if not api_key:
        raise ValueError("API Key is required for Upstage Document Reader.")

    Validates the provided API key.

    Args:
        api_key (str): The API key to be validated.

    Raises:
        ValueError: If the API key is empty or None.

    Returns:
        None

    
llama-index-integrations/readers/llama-index-readers-upstage/llama_index/readers/upstage/base.py