code: private void overrideViolationMessageIfNecessary(List<Violation> violations) {
          if (violationMessage != null && violations != null) {
              for (Violation violation : violations) {
                  violation.setMessage(violationMessage);
              }
          }
      }
docs: If the violationMessage property of this rule has been set, then use it to set the
  message within each violation, overriding the original message(s), if any.