docs: public DateTimeFormatter toFormatter() {
          Object f = getFormatter();
          InternalPrinter printer = null;
          if (isPrinter(f)) {
              printer = (InternalPrinter) f;
          }
          InternalParser parser = null;
          if (isParser(f)) {
              parser = (InternalParser) f;
          }
          if (printer != null || parser != null) {
              return new DateTimeFormatter(printer, parser);
          }
          throw new UnsupportedOperationException("Both printing and parsing not supported");
      }