title: Doctrine ORM Manager named "" does not exist
body: <p>I have a trouble while creating new entity in my Custom CMS Bundle . At the end of generating through this error : </p>
  
  <blockquote>
    <p>[InvalidArgumentException]<br>
     Doctrine ORM Manager named "" does not exist.</p>
  </blockquote>
  
  <p>However , I have tried to solve  <a href="https://stackoverflow.com/questions/14409342/invalid-argument-exception-when-generating-entities-from-existing-database">this way</a> . 
   But in this case I got another error : </p>
  
  <blockquote>
    <p>ClassNotFoundException in DoctrineExtension.php line 432:
    Attempted to load class "Version" from namespace "Doctrine\ORM".
    Did you forget a "use" statement for e.g. "Jackalope\Version\Version", "Doctrine\DBAL\Version", "Symfony\Component\Intl\Util\Version", "Doctrine\ODM\PHPCR\Version", "Doctrine\Common\Cache\Version" or "Doctrine\Common\Version"?</p>
  </blockquote>
  
  <p>What shold I do ? how to fix that ? </p>