private static final String oldConvertPattern(String pattern) {
        if (pattern == null) {
            return "";
        }
        String convertedPattern = pattern;
        for (PatternConverter converter : PATTERN_CONVERTERS) {
            convertedPattern = converter.convert(convertedPattern);
        }
        return convertedPattern;
    }
Checks that the pattern is converted the same way as before PF 9
primefaces/src/test/java/org/primefaces/convert/DateTimePatternConverterTest.java