By following the Templates section on Best Practices book, I should have the following code in my controller:

public function indexAction()
{
    return $this->render('default/index.html.twig');
}

This throw the following exception:

Template name "default/index.html.twig" is not valid (format is "bundle:section:template.format.engine").

I'm using "symfony/symfony": "2.6.*".

I think the template path validator should be reviewed, isn't it ?

Thanks.