diff --git a/src/Executor/Executor.php b/src/Executor/Executor.php
index 1a04e2f26e..e0e40f0169 100644
--- a/src/Executor/Executor.php
+++ b/src/Executor/Executor.php
@@ -188,7 +188,7 @@ class Executor
         array $headers,
         float $cpus,
         int $memory,
-        string $runtimeEntrypoint = null,
+        string $runtimeEntrypoint = '',
         bool $logging,
         int $requestTimeout = null
     ) {