def METHOD_NAME(self, nb):
    """
    Get the assignment name in the metadata of the provided notebook, if any.
    Args:
        nb (``nbformat.NotebookNode``): the notebook
    Returns:
        ``str | None``: the assignment name of the notebook, if any
    """
    if NOTEBOOK_METADATA_KEY not in nb["metadata"]:
        return None
    return nb["metadata"][NOTEBOOK_METADATA_KEY].get("assignment_name", None)