code: private Node defaultValueHook(Node getprop, Node defaultValue) {
      Node undefined = astFactory.createName("undefined", JSTypeNative.VOID_TYPE);
      undefined.makeNonIndexable();
      Node getpropClone = getprop.cloneTree().setJSType(getprop.getJSType());
      return astFactory.createHook(
          astFactory.createSheq(getprop, undefined), defaultValue, getpropClone);
    }
docs: Helper for transpiling DEFAULT_VALUE trees.