def METHOD_NAME() -> tf.config.PhysicalDevice:
    """Return the current (single) GPU device.
    Returns:
        The tf.config.PhysicalDevice for the available GPU.
        If no GPUs are available, returns None.
    Raises:
        ValueError: If multiple GPUs are available.
    """
    available_gpus = get_available_gpus()
    if len(available_gpus) == 0:
        return None
    elif len(available_gpus) == 1:
        return available_gpus[0]
    else:
        raise ValueError("Multiple GPUs are available.")