code: private static boolean matchLabel(Node target, String label) {
      if (label == null) {
        return true;
      }
      while (target.isLabel()) {
        if (target.getFirstChild().getString().equals(label)) {
          return true;
        }
        target = target.getParent();
      }
      return false;
    }
docs: Check if label is actually referencing the target control structure. If
  label is null, it always returns true.