code: private void validateDefaultValue(Node n) {
      if (n.isDefaultValue() && n.getParent().isParamList()) {
        Node targetNode = n.getFirstChild();
        JSDocInfo info = targetNode.getJSDocInfo();
        if (info == null) {
          return;
        }
  
        JSTypeExpression typeExpr = info.getType();
        if (typeExpr == null) {
          return;
        }
  
        Node typeNode = typeExpr.getRoot();
        if (typeNode.getToken() != Token.EQUALS) {
          report(typeNode, DEFAULT_PARAM_MUST_BE_MARKED_OPTIONAL);
        }
      }
    }
docs: Check that a parameter with a default value is marked as optional.
  TODO(bradfordcsmith): This is redundant. We shouldn't require it.