O
addGroup método tem a dica de tipo errado:Deveria ser:
/**
* Add groups
*
* @param \Blogger\BlogBundle\Entity\Group $groups
* @return User
*/
public function addGroup(\Blogger\BlogBundle\Entity\Group $groups)
{
$this->groups[] = $groups;
return $this;
}
Aviso
\Blogger\BlogBundle\Entity\Group em vez de \Blogger\BlogBundle\Entity\groups . 
