diff --git a/src/Service/BookingEditDraftService.php b/src/Service/BookingEditDraftService.php
index 3e6889a..d5f5780 100644
--- a/src/Service/BookingEditDraftService.php
+++ b/src/Service/BookingEditDraftService.php
@@ -431,9 +431,9 @@ class BookingEditDraftService
     /**
      * Resolves an insurance ID to an Insurance object.
      */
-    private function resolveInsurance(?int $insuranceId, Travel $travel): ?object
+    private function resolveInsurance(?string $insuranceId, Travel $travel): ?object
     {
-        if (null === $insuranceId) {
+        if (null === $insuranceId || '' === $insuranceId) {
             return null;
         }