def _update_with_merge_lists(self, other, key, val=None, **options):
    """
    Similar to _update_with_merge but merge lists always.

    :param self: mapping object to update with 'other'
    :param other: mapping object to update 'self'
    :param key: key of mapping object to update
    :param val: value to update self alternatively

    :return: None but 'self' will be updated
    """
    _update_with_merge(self, other, key, val=val, merge_lists=True, **options)