public <T> T getFirstValue(final String key, final T defaultValue, final Func1<String, T> converter) {
        final List<String> values = get(key);
        return values != null && !values.isEmpty() ? converter.call(values.get(0)) : defaultValue;
    }
IF this config has only one single String value then this value is returned. Otherwise null is returned
main/src/main/java/cgeo/geocaching/utils/config/LegacyFilterConfig.java