Fatal error after installing module And site is down

I am facing the same issue for 1.0.0-rc8

Following code will resolve the issue. Update this code in the getCustomMenuContent() function in CustomAdminMenuManager.php
<?php
// Filter allowed items.
    if (isset($buildArray['#items']) && is_array($buildArray['#items'])) {
      $this->customAdminMenuMenuItemDisplayManager->filterItems($buildArray['#items']);
    // Add toolbar-icon class.
      $this->initClasses($buildArray['#items']);
    }
?>

Automatically closed - issue fixed for 2 weeks with no activity.