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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _migrate0to1(previous: Mapping[str, Any]) -> SettingsMap: """ Migrate to version 1 of the feature flags file. Replaces old IDs with new IDs and sets any False values to None """

    next: SettingsMap = {}

    for s in settings:
        id = s.id
        old_id = s.old_id

        if previous.get(id) is True:
            next[id] = True
        elif previous.get(old_id) is True:
            next[id] = True
        else:
            next[id] = None

    return next