public static String formatPercentage(final OptionalDouble optPct) {
        return optPct != null && optPct.isPresent()
                ? ((long) optPct.getAsDouble()) + "%"
                : "?";
    }
@return An integer percentage suffixed with '%' or '?'
stroom-core-client/src/main/java/stroom/util/client/DataGridUtil.java