docs: private static DateTimeFormatter createFormatterForPattern(String pattern) {
          if (pattern == null || pattern.length() == 0) {
              throw new IllegalArgumentException("Invalid pattern specification");
          }
          DateTimeFormatter formatter = cPatternCache.get(pattern);
          if (formatter == null) {
              DateTimeFormatterBuilder builder = new DateTimeFormatterBuilder();
              parsePatternTo(builder, pattern);
              formatter = builder.toFormatter();
              if (cPatternCache.size() < PATTERN_CACHE_SIZE) {
                  // the size check is not locked against concurrent access,
                  // but is accepted to be slightly off in contention scenarios.
                  DateTimeFormatter oldFormatter = cPatternCache.putIfAbsent(pattern, formatter);
                  if (oldFormatter != null) {
                      formatter = oldFormatter;
                  }
              }
          }
          return formatter;
      }