getUrlObject() returning empty proto object

Question

I'm trying to follow this post to turn my menu tree into an array I can more easily work with.

When I run my code and look at $filteredArray I get:

title: *Name here*
url_obj: {}
has_children: true

I'm mostly working in THEME.theme page in:

function THEME_page_attachments_alter {
  $filteredArray = array();
  $menu_tree_service = \Drupal::service('menu.link_tree');

  $menu_parameters = new \Drupal\Core\Menu\MenuTreeParameters();
  $menu_parameters->excludeRoot();
  $menu_parameters->onlyEnabledLinks();

  $tree = $tree = $menu_tree_service->load('main', $menu_parameters);
  foreach ($tree as $item) {
    $itemObject = (object) ['title' => '', 'url_obj' => '', 'has_children' => ''];

    $itemObject->title = $item->link->getTitle();
    $itemObject->url_obj = $item->link->getUrlObject();
    $itemObject->has_children = $item->hasChildren;

    array_push($filteredArray, $itemObject);
  }
  $page['#attached']['drupalSettings']['mobileMenu']['menuTree'] = $tree;
  $page['#attached']['drupalSettings']['mobileMenu']['filteredArray'] = $filteredArray;
}

So it looks like it is grabbing the pages and returning them and looking at the docs I should be able to just call $item->link->getUrlObject(); to get the url so I'm not sure where I am going wrong.

Any pointers are appreciated, thanks!

Edit

Thanks to @stevekeiretsu for the pointers I have updated my code to:

1. Stringify getUrlObject:

   $itemObject->url_obj = $item->link->getUrlObject()->toString();

2. JSON encode $filteredArray before it is added to Drupal Settings:

   $page['#attached']['drupalSettings']['mobileMenu']['filteredArray'] = json_encode($filteredArray);

I am still getting an empty url for the url_obj and I also noticed that on $tree's menu items each had an empty object for 'link', so that I could see that leading to an empty url but then I do not understand why I am able to get the title of each of the menu items.

Thanks again!

Edit 2

It looks like this might have been an existing issue: https://www.drupal.org/project/drupal/issues/2642602

I'm really new to Drupal so I'm not sure about this.