def path_does_not_exist(row):
    """
    Check whether any paths exist between the source and target. We know there
    isn't a path if the row has a zero path count, or has a zero dwpc if the path
    count isn't present in the row
    """
    if "path_count" in row:
        return row["path_count"] == 0
    return row["dwpc"] == 0