Properly support empty response content

camel/Extraction/Response.php

@@ -17,7 +17,7 @@ class Response extends BaseDTO
 
     public function __construct(array $parameters = [])
     {
-        if (is_array($parameters['content'])) {
+        if (is_array($parameters['content'] ?? null)) {
             $parameters['content'] = json_encode($parameters['content']);
         }