Creating a CategoryGroup in a migration - Exception: Tried to save a category group that is missing site settings

Description

When trying to create a new CategoryGroup within a migration, the migration fails with an error saying it cannot save a category group which is missing site settings:

Exception: Tried to save a category group that is missing site settings (/project/vendor/craftcms/cms/src/services/Categories.php:325)

Here the code for my migration file

public function safeUp()
    {
        $siteId = Craft::$app->sites->getPrimarySite()->id;

        $blogCategoryGroup = new \craft\models\CategoryGroup([
            "name" => "Blog Categories",
            "handle" => "blogCategories",
        ]);
        $blogCatSettings = new \craft\models\CategoryGroup_SiteSettings([
            "siteId" => $siteId,
            "uriFormat" => "/category/{slug}",
            "template" => "/category/_entry",
            "hasUrls" => 1,
        ]);
        $blogCategoryGroup->setSiteSettings([$blogCatSettings]);
        return Craft::$app->categories->saveGroup($blogCategoryGroup);
    }

I have also tried setting the settings directly, which worked when creating a new Section:

$blogCategoryGroup = new \craft\models\CategoryGroup([
    "name" => "Blog Categories",
    "handle" => "blogCategories",
    "siteSettings" => [
        new \craft\models\CategoryGroup_SiteSettings([
            "siteId" => $siteId,
            "uriFormat" => "/category/{slug}",
            "template" => "/category/_entry",
            "hasUrls" => 1,
        ])
    ]
]);

The error comes from the categories service here:

// Make sure they're all there
foreach (Craft::$app->getSites()->getAllSiteIds() as $siteId) {
    if (!isset($allSiteSettings[$siteId])) {
        throw new Exception('Tried to save a category group that is missing site settings');
    }
}

Here is the dump from Craft::$app->getSites()->getAllSiteIds():

array(1) {
  [0]=>
  int(1)
}

It seems to me that it's searching for a siteSettings object at the index of the siteId (1), but when I dump the $allSiteSettings, there is no item at $allSiteSettings[1] because the siteSettings is a zero-indexed array:

array(1) {
    [0]=>
    object(craft\models\CategoryGroup_SiteSettings)#147 (13) {
      ["id"]=>
      NULL
      ["groupId"]=>
      NULL
      ["siteId"]=>
      string(1) "1"
      ["hasUrls"]=>
      int(1)
      ["uriFormat"]=>
      string(16) "/category/{slug}"
      ["template"]=>
      string(16) "/category/_entry"
      ["_group":"craft\models\CategoryGroup_SiteSettings":private]=>
      *RECURSION*
      ["_errors":"yii\base\Model":private]=>
      NULL
      ["_validators":"yii\base\Model":private]=>
      NULL
      ["_scenario":"yii\base\Model":private]=>
      string(7) "default"
      ["_events":"yii\base\Component":private]=>
      array(0) {
      }
      ["_eventWildcards":"yii\base\Component":private]=>
      array(0) {
      }
      ["_behaviors":"yii\base\Component":private]=>
      NULL
    }
  }

Steps to reproduce

1. Create a new migration
2. Try to create a new CategoryGroup inside the safeUp method
3. Run .craft migrate/up
4. Receive Exception

Additional info

• Craft version: 3.0.0-RC17
• PHP version: 7.1.12
• Database driver & version: MySQL 5.6.38
• Plugins & versions: Redactor 1.0.1

Start in vendor/craftcms/cms/src/services/Categories.php around line 325, then inspect how CategoryGroup site settings are assembled and keyed during saveGroup(). Reproduce the migration from the issue with Craft 3.0.0-RC17 and verify that saving a group with the primary site's settings no longer raises the missing-site-settings exception.