def join_string_lists(**kwargs) -> dict:
    """Convert named lists of strings to one dict with comma-separated strings.

    :param kwargs: Lists of strings
    :return: Converted dict.

    Example:

    >>> join_string_lists(foo=["a", "b", "c"], bar=["a", "b"], foobar=None)
    {"foo": "a,b,c", "bar": "a,b"}
    """
    return {k: ",".join(v) for k, v in kwargs.items() if v}