static String serializeFlags(Iterable<Flag> flags) { List<Flag> extraFlags = new ArrayList<>(); for (Flag flag : flags) { switch (flag) { case DELETED: case SEEN: case FLAGGED: case ANSWERED: case FORWARDED: { break; } default: { extraFlags.add(flag); } } } return Utility.combine(extraFlags, ',').toUpperCase(Locale.US); }