Type resolvers are not called on mutation results?

[brunoreis]

I have this query:

mutation{
    registerThread(message_ids:[302]){
        thread {
            id
        }
        messagesStatus{
            cleanMessagesCount
        }
    }
}

This is the RegisterThreadField definition:

class RegisterThreadField extends AbstractContainerAwareField
{
    /**
     * @return ThreadType
     */
    public function getType()
    {
        return new ObjectType([
            'name'   => 'RegisterThreadMutationType',
            'fields' => [
                'thread' => [
                    'type' => new ThreadType()
                ],
                'messagesStatus' => [
                    'type' => new MessagesStatusType()
                ]
            ]
        ]);
    }

    public function build(FieldConfig $config)
    {
        $config->addArguments([
            'message_ids' => new ListType(
                new IdType()
            )
         ]);
    }

    public function resolve($value, array $args, ResolveInfo $info)
    {
        return $this->container
            ->get('app.resolver.register_thread')
            ->resolve(new ParameterBag($args));
    }

And this is the MessagesStatusType

class MessagesStatusType extends AbstractObjectType
{
    /**
     * @param \Youshido\GraphQL\Config\Object\ObjectTypeConfig $config
     */
    public function build($config)
    {
        $config->addFields([
            'id' => new IdType(),
            'oldestMessageDate' => [
                'type'    => new DateTimeType(),
                'resolve' => ['@app.resolver.messages_status','oldestMessageDate']
            ],
            'newestMessageDate' => [
                'type'    => new DateTimeType(),
                'resolve' => ['@app.resolver.messages_status','newestMessageDate']
            ],
            'messagesCount' => [
                'type'    => new IntType(),
                'resolve' => ['@app.resolver.messages_status','messagesCount']
            ],
            'cleanMessagesCount' => [
                'type'    => new IntType(),
                'resolve' => ['@app.resolver.messages_status','cleanMessagesCount']
            ]
        ]);
    }

The resolver result does not return an index for the messagesStatus field of the query. But, I was expecting that the custom resolvers defined on the MessagesStatusType would take care of that. But it seem that they are not being called.

This is the result:

{
    "data": {
        "registerThread": {
            "thread": {
                "id": "43"
            },
            "messagesStatus": null
        }
    }
}

Should those resolvers (declared as callable services) on the MessagesStatusType class have being called?