Doctrine\MongoDB\Query\Expr::exists PHP Method

    public function exists($bool)
    {
        return $this->operator('$exists', (bool) $bool);
    }

 /**
  * Specify $exists criteria for the current field.
  *
  * @see Expr::exists()
  * @see http://docs.mongodb.org/manual/reference/operator/exists/
  * @param boolean $bool
  * @return self
  */
 public function exists($bool)
 {
     $this->expr->exists((bool) $bool);
     return $this;
 }