Fix ServiceMethodsSubscriberTrait for nullable service

Author: StevenRenaux

ServiceSubscriberTrait.php

@@ -51,7 +51,7 @@ public static function getSubscribedServices(): array
             $attribute = $attribute->newInstance();
             $attribute->key ??= self::class.'::'.$method->name;
             $attribute->type ??= $returnType instanceof \ReflectionNamedType ? $returnType->getName() : (string) $returnType;
-            $attribute->nullable = $returnType->allowsNull();
+            $attribute->nullable = $attribute->nullable ?: $returnType->allowsNull();
 
             if ($attribute->attributes) {
                 $services[] = $attribute;