fix: parameter not found when no value (#6458)

src/Metadata/Parameter.php

@@ -14,6 +14,7 @@
 namespace ApiPlatform\Metadata;
 
 use ApiPlatform\OpenApi;
+use ApiPlatform\State\ParameterNotFound;
 use ApiPlatform\State\ParameterProviderInterface;
 use Symfony\Component\Validator\Constraint;
 
@@ -107,7 +108,7 @@ public function getConstraints(): Constraint|array|null
      */
     public function getValue(): mixed
     {
-        return $this->extraProperties['_api_values'] ?? null;
+        return $this->extraProperties['_api_values'] ?? new ParameterNotFound();
     }
 
     /**