def validate_series(charm, linter):
    """Validate supported series list in charm metadata.

    We don't validate the actual series names because:

    1. `charm push` does that anyway
    2. our list of valid series would be constantly falling out-of-date

    :param charm: dict of charm metadata parsed from metadata.yaml
    :param linter: :class:`CharmLinter` object to which info/warning/error
        messages will be written

    """
    if 'series' not in charm:
        linter.err('missing series: must be a list of series names')
    elif not isinstance(charm['series'], list):
        linter.err('series: must be a list of series names')
