Doctrine DQL query produces Error: Expected Literal, got end of string - symfony

Question

I am currently trying to build a blog website following a course that uses
Symfony 2.5.2. (PHP -v 7.0)
To retrieve a post I am using a following Controller
/**
* #Route(
* "/{slug}",
* name = "blog_post"
* )
* #Template()
*/
public function postAction($slug)
{
$PostRepo = $this->getDoctrine()->getRepository('AniaBlogBundle:Post');
$Post = $PostRepo->getPublishedPost($slug);
if(null === $Post){
throw $this->createNotFoundException('Post not found');
}
return array(
'post'=> $Post
);
}
and here is my getPublishedPost function :
public function getPublishedPost($slug){
$qb = $this->getQueryBuilder(array(
'status' => 'published'
));
$qb->andWhere('p.slug = :slug')
->setParameter('slug', $slug);
return $qb->getQuery()->getOneOrNullResult();
}
and getQueryBuilder function :
public function getQueryBuilder(array $params = array()){
$qb = $this->createQueryBuilder('p')
->select('p, c, t')
->leftJoin('p.category', 'c')
->leftJoin('p.tags', 't');
if(!empty($params['status'])){
if('published' == $params['status']){
$qb->where('p.publishedDate <= :currDate AND p.publishedDate IS NOT NULL')
->setParameter('currDate', new \DateTime());
}else if('unpublished' == $params['status']) {
$qb->where('p.publishedDate > :currDate OR p.publishedDate IS NULL')
->setParameter('currDate', new \DateTime());
}
}
if(!empty($params['orderBy'])){
$orderDir = !empty($params['orderDir']) ? $params['orderDir'] : NULL;
$qb->orderBy($params['orderBy'], $orderDir);
}
if(!empty($params['categorySlug'])){
$qb->andWhere('c.slug = :categorySlug')
->setParameter('categorySlug', $params['categorySlug']);
}
if(!empty($params['tagSlug'])){
$qb->andWhere('t.slug = :tagSlug')
->setParameter('tagSlug', $params['tagSlug']);
}
if(!empty($params['search'])) {
$searchParam = '%'.$params['search'].'%';
$qb->andWhere('p.title LIKE :searchParam OR p.content LIKE :searchParam')
->setParameter('searchParam', $searchParam);
}
return $qb;
}
}
However i get the 500 error saying : [Syntax Error] line 0, col -1: Error: Expected Literal, got end of string.
Thank you in advance for any suggestions!