Проблема с библиотекой Codeigniter mailchimp

Я вижу эту ошибку, когда пытаюсь вызвать функцию из библиотеки mailchimp.

    A PHP Error was encountered

Severity: Notice

Message: Undefined property: Api::$Mailchimp

Filename: controllers/api.php

Line Number: 13


Fatal error: Call to a member function call() on a non-object in /home/upul/public_html/mailchimp/application/controllers/api.php on line 13

Я сделал все соответственно. Я не знаю, почему библиотека не создает экземпляр. Я знаю, что означает эта ошибка, но не вижу причины, по которой она появляется

Моя библиотека (библиотеки / Mailchimp.php)

    class Mailchimp
{
private $api_key;
private $api_endpoint = 'https://<dc>.api.mailchimp.com/2.0/';
/**
* Create a new instance
*/
public function __construct()
{
$this->ci =& get_instance();
$this->ci->load->config('mailchimp');
$this->api_key = $this->ci->config->item('api_key');
$this->api_endpoint = $this->ci->config->item('api_endpoint');
list(, $datacentre) = explode('-', $this->api_key);
$this->api_endpoint = str_replace('<dc>', $datacentre, $this->api_endpoint);
}
/**
* Call an API method. Every request needs the API key, so that is added automatically -- you don't need to pass it in.
* @param  string $method The API method to call, e.g. 'lists/list'
* @param  array  $args   An array of arguments to pass to the method. Will be json-encoded for you.
* @return array          Associative array of json decoded API response.
*/
public function call($method, $args=array())
{
return $this->_raw_request($method, $args);
}
/**
* Performs the underlying HTTP request. Not very exciting
* @param  string $method The API method to be called
* @param  array  $args   Assoc array of parameters to be passed
* @return array          Assoc array of decoded result
*/
private function _raw_request($method, $args=array())
{
$args['apikey'] = $this->api_key;
$url = $this->api_endpoint.'/'.$method.'.json';
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-Type: application/json'));
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_TIMEOUT, 10);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($args));
$result = curl_exec($ch);
curl_close($ch);
return $result ? json_decode($result, true) : false;
}
}

Мой контроллер (controllers / api.php)

    class Api extends CI_Controller {

public function __construct()
{
parent::__construct();
$this->load->library('Mailchimp');
}

public function index()
{
$lists = $this->Mailchimp->call('lists/list');
echo $lists;
}
}