def fqn(package_name: str, class_name: str) -> str:
    """Return the fully qualified name (Java style) of the class.

    Args:
        package_name: Name of the package. The default package should be an
            empty string.
        class_name: Canonical name of the class.
    Returns:
        The fully qualified name of the class.
    """
    return (
        class_name
        if not package_name
        else "{}.{}".format(package_name, class_name)
    )