refactor: handle exception on vault unlock date check for validation

backend/letters/migrations/0009_alter_letter_notified_at_alter_letter_unlock_at.py

@@ -0,0 +1,22 @@
+# Generated by Django 6.0.4 on 2026-04-17 18:08
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("letters", "0008_letter_notified_at"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="letter",
+            name="notified_at",
+            field=models.DateTimeField(blank=True, db_index=True, null=True),
+        ),
+        migrations.AlterField(
+            model_name="letter",
+            name="unlock_at",
+            field=models.DateTimeField(blank=True, db_index=True, null=True),
+        ),
+    ]

backend/letters/serializers.py

@@ -39,11 +39,14 @@ class LetterSerializer(serializers.ModelSerializer):
     def to_representation(self, instance):
         fields = super().to_representation(instance)
         if fields["type"] == Letter.Type.VAULT and fields["status"] == Letter.Status.SEALED:
+            try:
                 unlock_datetime = datetime.fromisoformat(fields["unlock_at"]).replace(tzinfo=UTC)
                 if unlock_datetime - datetime.now(tz=UTC) > timedelta(seconds=0):
                     fields["encrypted_content"] = None
                     fields["images"] = None
                     fields["encrypted_dek"] = None
+            except (ValueError, TypeError):
+                pass
         return fields
 
     def validate(self, data):
@@ -54,4 +57,6 @@ class LetterSerializer(serializers.ModelSerializer):
             raise serializers.ValidationError(
                 "encrypted_dek is required when encrypted_content and encrypted_metadata are present"
             )
+        if data.get("type") == Letter.Type.VAULT and not data.get("unlock_at"):
+            raise serializers.ValidationError("unlock_at is required for vault letters")
         return data