Zend\Expressive\Application::getEmitter PHP Method

    public function getEmitter()
    {
        if (!$this->emitter) {
            $this->emitter = new Emitter\EmitterStack();
            $this->emitter->push(new SapiEmitter());
        }
        return $this->emitter;
    }

 private function initResponseCollector()
 {
     /**
      * @var Zend\Expressive\Emitter\EmitterStack
      */
     $emitterStack = $this->application->getEmitter();
     while (!$emitterStack->isEmpty()) {
         $emitterStack->pop();
     }
     $this->responseCollector = new ZendExpressiveConnector\ResponseCollector();
     $emitterStack->unshift($this->responseCollector);
 }