def METHOD_NAME(data):
    """Return the number of keywords.
    Arguments
    ---------
    data: asreview.data.ASReviewData
        An ASReviewData object with the records.
    Return
    ------
    int:
        The statistic
    """
    if data.keywords is None:
        return None
    return np.average([len(keywords) for keywords in data.keywords])