Twig Extension with ContainerInterface injected

UniversityExtension.php

<?php

class UniversityExtension extends \Twig_Extension
{
    private $container;

    /**
     * An internal cache used to prevent creating this chain loader multiple times
     */
    private $twigChainLoader;

    public function __construct(ContainerInterface $container)
    {
        $this->container = $container;
    }

    /**
     * {@inheritdoc}
     */
    public function getTests()
    {
        return array(
            'paid' => new \Twig_Test_Method($this, 'isPaid'),
            'viewed' => new \Twig_Test_Method($this, 'isViewed'),
            'solved' => new \Twig_Test_Method($this, 'isSolved'),
        );
    }

    /**
     * {@inheritdoc}
     */
    public function getFunctions()
    {
        return array(
            'absolute_asset' => new \Twig_Function_Method($this, 'getAbsoluteAssetUrl'),
            'get_template'  => new \Twig_Function_Method($this, 'getTemplate', array('is_safe' => array('html'))),
            new \Twig_SimpleFunction('get_client_template', array($this, 'getClientTemplate'), array('is_safe' => array('html'))),
            new \Twig_SimpleFunction('get_comment_count', array($this, 'getCommentCount')),

            new \Twig_SimpleFunction('get_main_contributor', array($this, 'getMainContributor')),
            new \Twig_SimpleFunction('get_other_contributors', array($this, 'getOtherContributors')),
            new \Twig_SimpleFunction('get_all_contributors', array($this, 'getAllContributors')),
            new \Twig_SimpleFunction('get_chapter_number', array($this, 'getChapterNumber')),
            new \Twig_SimpleFunction('get_next_url', array($this, 'getNextUrl')),
            new \Twig_SimpleFunction('get_new_order', array($this, 'getNewOrder')),
            new \Twig_SimpleFunction('get_stripe_public_key', array($this, 'getStripePublicKey')),
            new \Twig_SimpleFunction('get_last_subscription_order', array($this, 'getLastSubscriptionOrder')),
            new \Twig_SimpleFunction('get_current_order', array($this, 'getCurrentOrder')),
        );
    }

    public function getFilters()
    {
        return array(
            new \Twig_SimpleFilter('normalize', array($this, 'normalize')),
            new \Twig_SimpleFilter('format_price', array($this, 'formatPrice')),
            new \Twig_SimpleFilter('build_status_label', array($this, 'buildStatusLabel')),
            new \Twig_SimpleFilter('illustration_path', array($this, 'getBuildIllustrationPath')),
            new \Twig_SimpleFilter('build_highlight', array($this, 'highlightBuildNotes')),
            new \Twig_SimpleFilter('subscription_price', array($this, 'getSubscriptionPrice')),
            new \Twig_SimpleFilter('github_markdown', array($this, 'parseGitubMarkdown')),
            new \Twig_SimpleFilter('secure', array($this, 'makeUrlSecure')),
            new \Twig_SimpleFilter('asset_version', array($this, 'getAssetVersion')),
        );
    }


    public function normalize($object)
    {
        $normalizer = $this->container->get('normalizer');

        return $normalizer->normalize($object);
    }

    public function getMainContributor(Blog $blog)
    {
        $mainContributor = $this->getEntityManager()->getRepository('KnpUniversityBundle:BlogContributor')
            ->findMainContributor($blog)
        ;

        if (!$mainContributor) {
            throw new \Exception(sprintf('Could not find any contributors for blog "%s"', $blog->getId()));
        }

        return $mainContributor;
    }


    public function getAllContributors(Blog $blog)
    {
        $contributors = $this->getEntityManager()->getRepository('KnpUniversityBundle:BlogContributor')
            ->findAllContributors($blog)
        ;

        return $contributors;
    }

    public function getChapterNumber(CourseChapter $chapter)
    {
        return $this->getEntityManager()->getRepository('KnpUniversityBundle:CourseChapter')
            ->getChapterNumber($chapter)
        ;
    }

   
    public function getBuildIllustrationPath(CourseBuild $build)
    {
        return $this->container->get('knp_university.storage.public_storage')
            ->getIllustrationPublicPath($build)
        ;
    }

    public function getStripePublicKey()
    {
        return $this->container->get('knp_university.stripe.manager')
            ->getPublicKey();
    }

    public function parseGitubMarkdown($str)
    {
        return $this->container->get('markdown_parser')
            ->parse($str);
    }
}

Fatal error: Uncaught exception 'Symfony\Component\Debug\Exception\ContextErrorException' with message 'Catchable Fatal Error: Argument 1 passed to FrontBundle\Twig\FrontExtension::__construct() must be an instance of FrontBundle\Twig\ContainerInterface, none given