title: Syntax Error: line 0, col 81: Error: Expected Literal, got 'NULL'
body: <p>I got an error <code>[Syntax Error] line 0, col 81: Error: Expected Literal, got 'NULL'</code> when I try to execute query via query builder</p>
  
  <pre><code>        $qb = $this-&gt;createQueryBuilder('r')
              -&gt;select('r')
              -&gt;where('r.query = :query')
              -&gt;setParameter('query', $query)   
              -&gt;andWhere('r.lang = NULL')
          ;
  
          return $qb-&gt;getQuery()-&gt;getOneOrNullResult();
  </code></pre>
  
  <p><code>r.lang</code> field is defined as:</p>
  
  <pre><code>/**
   * @var integer
   *
   * @ORM\ManyToOne(targetEntity="\BW\LocalizationBundle\Entity\Lang")
   * @ORM\JoinColumn(name="lang_id", referencedColumnName="id")
   */
  private $lang;
  </code></pre>
  
  <p>Help to solve error, please</p>