add assert

Author: rez1dent3

src/Internal/Repository/TransferRepository.php

@@ -36,8 +36,7 @@ public function insertOne(TransferDtoInterface $dto): Transfer
     {
         $attributes = $this->transformer->extract($dto);
         $instance = $this->transfer->newInstance($attributes);
-        $instance->save();
-
+        assert($instance->save() === true);
         assert($instance->getKey() !== null);
 
         return $instance;