diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index ee1dae49..f17df61b 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -25,7 +25,7 @@ jobs:
         php-versions: ['8.1']
     steps:
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
       - name: Setup PHP, with composer and extensions
         uses: shivammathur/setup-php@v2
         with:
@@ -47,7 +47,7 @@ jobs:
         id: composer-cache
         run: echo "::set-output name=dir::$(composer config cache-files-dir)"
       - name: Cache composer dependencies
-        uses: actions/cache@v2
+        uses: actions/cache@v3
         with:
           path: ${{ steps.composer-cache.outputs.dir }}
           key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}
diff --git a/src/Domain/Model/Messaging/SubscriberList.php b/src/Domain/Model/Messaging/SubscriberList.php
index e8cf7886..b5d76aca 100644
--- a/src/Domain/Model/Messaging/SubscriberList.php
+++ b/src/Domain/Model/Messaging/SubscriberList.php
@@ -57,7 +57,7 @@ class SubscriberList implements DomainModel, Identity, CreationDate, Modificatio
     #[Ignore]
     protected ?DateTime $modificationDate = null;
 
-    #[ORM\Column(name: 'listorder', type: 'integer')]
+    #[ORM\Column(name: 'listorder', type: 'integer', nullable: true)]
     #[SerializedName('list_position')]
     #[Groups(['SubscriberList'])]
     private ?int $listPosition;
@@ -120,7 +120,7 @@ public function setDescription(string $description): void
         $this->description = $description;
     }
 
-    public function getListPosition(): int
+    public function getListPosition(): ?int
     {
         return $this->listPosition;
     }
@@ -130,7 +130,7 @@ public function setListPosition(int $listPosition): void
         $this->listPosition = $listPosition;
     }
 
-    public function getSubjectPrefix(): string
+    public function getSubjectPrefix(): ?string
     {
         return $this->subjectPrefix;
     }
diff --git a/src/Domain/Model/Subscription/Subscription.php b/src/Domain/Model/Subscription/Subscription.php
index a7fb89c3..f6381fdf 100644
--- a/src/Domain/Model/Subscription/Subscription.php
+++ b/src/Domain/Model/Subscription/Subscription.php
@@ -15,6 +15,7 @@
 use PhpList\Core\Domain\Model\Messaging\SubscriberList;
 use PhpList\Core\Domain\Model\Traits\CreationDateTrait;
 use PhpList\Core\Domain\Model\Traits\ModificationDateTrait;
+use Symfony\Component\Serializer\Attribute\Groups;
 
 /**
  * This class represents subscriber who can subscribe to multiple subscriber lists and can receive email messages from
@@ -57,6 +58,7 @@ class Subscription implements DomainModel, CreationDate, ModificationDate
     )]
     #[ORM\JoinColumn(name: 'listid', onDelete: 'CASCADE')]
     #[Ignore]
+    #[Groups(['SubscriberListMembers'])]
     private ?SubscriberList $subscriberList = null;
 
     public function getSubscriber(): Subscriber|Proxy|null
diff --git a/src/Domain/Repository/Subscription/SubscriberRepository.php b/src/Domain/Repository/Subscription/SubscriberRepository.php
index c467e9b6..86a66892 100644
--- a/src/Domain/Repository/Subscription/SubscriberRepository.php
+++ b/src/Domain/Repository/Subscription/SubscriberRepository.php
@@ -10,7 +10,7 @@
 /**
  * Repository for Subscriber models.
  *
- * @method Subscriber findOneByEmail(string $email)
+ * @method Subscriber|null findOneByEmail(string $email)
  *
  * @author Oliver Klee <oliver@phplist.com>
  */