code: protected Matcher generateMatcher(String regex, String valueString)
          throws TransformationOperationException {
          if (regex == null) {
              throw new TransformationOperationException("No regex defined. The step will be skipped.");
          }
          try {
              Pattern pattern = Pattern.compile(regex);
              return pattern.matcher(valueString);
          } catch (PatternSyntaxException e) {
              String message =
                  String.format("Given regex string %s can't be compiled. The step will be skipped.", regex);
              logger.warn(message);
              throw new TransformationOperationException(message);
          }
      }
docs: Generates a matcher for the given valueString with the given regular expression.