def get_query(event):
    """
    Get event signup query class.

    :param event: Target event to get query class from.
    :type event: core.models.Event
    :return: Query class or None if query class was not found.
    :rtype: T <= QueryBuilder
    """
    labour_meta = event.labour_event_meta
    if labour_meta is None:
        return None
    signup_extra = labour_meta.signup_extra_model
    return signup_extra.get_query_class()