Double Response On RuntimeException No application encryption key

i received double responses when i remove my application key and ran the application, follow these steps to replicate the bug

    composer create-project laravel/laravel "project-name"
    cd project-name
    nano .env

Delete the application key if any has been set

    APP_KEY=

save the .env file go to the Handler.php file and add the following

    cd App\Exceptions
    nano Handler.php

Add the following to the render function

    /**
     * Render an exception into an HTTP response.
     *
     * @param  \Illuminate\Http\Request  $request
     * @param  \Exception  $exception
     * @return \Illuminate\Http\Response
     */
    public function render($request, Exception $exception)
    {
        // Thrown when an exception occurs.
        if ($exception instanceof Exception) {
            return response()->json('okay', 500);
        }

        return parent::render($request, $exception);
    }

Then run on your browser visit http://127.0.0.1:8000/ or http://serving_address/ You should receive two json response instead of one

My question, is this a bug? should i not return json response from the handler? how do i fix this?