@Override public Set<String> upgrade(Map<String, Object> settings) { upgradeFolderEntry(settings, "archiveFolderName"); upgradeFolderEntry(settings, "autoExpandFolderName"); upgradeFolderEntry(settings, "draftsFolderName"); upgradeFolderEntry(settings, "sentFolderName"); upgradeFolderEntry(settings, "spamFolderName"); upgradeFolderEntry(settings, "trashFolderName"); return null; }