def listify(vars_dict: dict, key: str) -> dict:
    """
    Converts value of `key` in `vars` to a list via string split on "," character.
    If `key` is not present in `vars_dict`, an empty list is set as its value.
    """
    vars_dict[key] = vars_dict.get(key, "").split(",")
    return vars_dict