code: public static void appendToRule(StringBuffer rule,
                                      UnicodeMatcher matcher,
                                      boolean escapeUnprintable,
                                      StringBuffer quoteBuf) {
          if (matcher != null) {
              appendToRule(rule, matcher.toPattern(escapeUnprintable),
                           true, escapeUnprintable, quoteBuf);
          }
      }
docs: Given a matcher reference, which may be null, append its
  pattern as a literal to the given rule.