def join_summaries(*args):
    """
    Joins summaries. If summary value is not string, it will be ignored.

    :param str separator: Summary separator.
    :param list[str] args: List of summaries.
    :return: Joined strings.
    :rtype: str | None
    """
    summaries_strings = []
    """:type: list[str]"""
    for summary in args:
        if isinstance(summary, str) and len(summary) > 0:
            summaries_strings.append(summary)

    if len(summaries_strings) == 0:
        return None
    return ", ".join(summaries_strings)