'Retrieve an attribute from a course\'s "about" info'

@classmethod
def fetch_about_attribute(cls, course_key, attribute):

    if (attribute not in (ABOUT_ATTRIBUTES + ['video'])):
        raise ValueError("'{0}'    is    not    a    valid    course    about    attribute.".format(attribute))
    usage_key = course_key.make_usage_key('about', attribute)
    try:
        value = modulestore().get_item(usage_key).data
    except ItemNotFoundError:
        value = None
    return value
