diff --git a/lib/classes/JsonApi/Schemas/Courseware/Instance.php b/lib/classes/JsonApi/Schemas/Courseware/Instance.php
index ff109661a41c393e1075ead13d261de059994f22..c5224756844e161515901ec7fe04ac732b0c550a 100644
--- a/lib/classes/JsonApi/Schemas/Courseware/Instance.php
+++ b/lib/classes/JsonApi/Schemas/Courseware/Instance.php
@@ -26,6 +26,8 @@ class Instance extends SchemaProvider
 
     /**
      * {@inheritdoc}
+     *
+     * @param \Courseware\Instance $resource
      */
     public function getAttributes($resource, ContextInterface $context): iterable
     {
diff --git a/lib/models/Courseware/Instance.php b/lib/models/Courseware/Instance.php
index 5cff95314bd02bd07808e816b7d234083179eed1..97990f6a58aa376f5087577086bfe92363936be5 100644
--- a/lib/models/Courseware/Instance.php
+++ b/lib/models/Courseware/Instance.php
@@ -284,7 +284,11 @@ class Instance
      */
     public function isValidCertificateSettings($certificateSettings): bool
     {
-        return (int) $certificateSettings['threshold'] >= 0 && (int) $certificateSettings['threshold'] <= 100;
+        return !isset($certificateSettings['threshold'])
+            || (
+                $certificateSettings['threshold'] >= 0
+                && $certificateSettings['threshold'] <= 100
+            );
     }
 
     private function validateCertificateSettings($certificateSettings): void
@@ -335,7 +339,7 @@ class Instance
      */
     public function isValidReminderSettings($reminderSettings): bool
     {
-        $valid = in_array($reminderSettings['interval'], [0, 7, 14, 30, 90, 180, 365]);
+        $valid = in_array($reminderSettings['interval'] ?? 0, [0, 7, 14, 30, 90, 180, 365]);
 
         return $valid;
     }
@@ -388,7 +392,7 @@ class Instance
      */
     public function isValidResetProgressSettings($resetProgressSettings): bool
     {
-        $valid = in_array($resetProgressSettings['interval'], [0, 14, 30, 90, 180, 365]);
+        $valid = in_array($resetProgressSettings['interval'] ?? 0, [0, 14, 30, 90, 180, 365]);
 
         return $valid;
     }