diff --git a/RdKafkaProducer.php b/RdKafkaProducer.php
index 64b9ea3..69411df 100644
--- a/RdKafkaProducer.php
+++ b/RdKafkaProducer.php
@@ -121,5 +121,7 @@ public function flush(int $timeout): ?int
         if (method_exists($this->producer, 'flush')) {
             return $this->producer->flush($timeout);
         }
+
+        return null;
     }
 }