message: fix NULL/null mismatch
diff: @@ -65,7 +65,7 @@ Expr * Expr::ARRAY(std::vector<Expr*> arr) {
  auto _arr = new std::vector<Symbol>();
  for (auto item : arr) {
  _arr->push_back(*dynamic_cast<Symbol*>(item->data));
  - item->data = null;
  + item->data = NULL;
  delete item;
  }
  