def _get_lines_from_file(filename, lines=None):
    """
    If lines is None read the lines from the file with the filename filename.

    Args:
        filename (str): file to read lines from
        lines (list/ None): list of lines

    Returns:
        list: list of lines
    """
    if lines is None:
        with open(filename, "r") as f:
            lines = f.readlines()
    return lines