diff --git a/src/ai-bundle/config/options.php b/src/ai-bundle/config/options.php
index 0ad9e775f..085d13e66 100644
--- a/src/ai-bundle/config/options.php
+++ b/src/ai-bundle/config/options.php
@@ -882,7 +882,7 @@
                             ->end()
                             ->beforeNormalization()
                                 ->always(function ($v) {
-                                    if (\is_string($v)) {
+                                    if (\is_string($v) || null === $v) {
                                         return $v;
                                     }