PHP script doesn't stop after error

I am using CodeIgniter framework and After testing in XAMPP, a normal error like "Missing argument" the php script stops and it shows me the PHP Warning page, however in the hosting server(e.g. GoDaddy) the php script takes a while to stop and it shows me the 500 error page, consequently the server has a new Entry Process.

Any idea? Thanks!

   public function getAQByLocation($city) {
        $this->load->helper('url');
        $ch = curl_init();

        curl_setopt($ch, CURLOPT_URL, "http://api.waqi.info/feed/$city/?
        token=" . $this->AQ_API_KEY);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);

        $result = curl_exec($ch);

        if (curl_errno($ch)) {
            echo 'Error:' . curl_error($ch);
        }
        curl_close ($ch);

        echo $result;
    }

This is the code, to simulate that error i just omitted the parameter $city, e.g. xxx.com/Home/getAQByLocation