src/Application/SimpleApplication.php
public function responder(ResponderInterface $responder = null) : ResponderInterface
    {
        if ($responder){
            $this->responder = $responder;
        }
        if (!$this->responder){
            $this->responder = new NullResponder();
        }
        return $this->responder;
    }
public function responder(ResponderInterface $responder = null) : ResponderInterface
    {
        if ($responder){
            $this->responder = $responder;
        }
        if (!$this->responder){
            $this->responder = new NullResponder();
        }
        return $this->responder;
    }
Set/get responder

@param ResponderInterface $responder

@return ResponderInterface