Symfony Twig {{render}} handling passed arguments: Cannot get a different value [duplicate]

Over a template I do a render method:

 {% set someString = "non-default" %}

{{ render(controller('AppBundle:Widgets:myCapsWidget'),{'somestring':someString})  }}

Over the controller I have the following method:

public function myCapsWidgetAction()
{
  //@todo: access the passing parameter
}

My problem is how can I access the somestring parameter? I tried to do

public function myCapsWidgetAction($somestring="default")
{
  return new Response(strtoupper($somestring));
}

Then via xdebug I noticed that the passed parameter was default instead of non-default.

I also looked over theese links:

• symfony twig render controller argument array
• https://knpuniversity.com/screencast/symfony2-ep3/render-controller

But still no light in my path.