def clean_question_mark(content):
    """Removes question mark strings, turning them to nulls.

    Parameters
    ----------
    content: :class:`str`
        A string to clean.

    Returns
    -------
    :class:`str`
        The string, or None if it was a question mark.
    """
    if not content:
        return None
    if '?' in content:
        return None
    return content.strip()
