Symfony Model返回null而不是class

When I attempt to load my database results, it doesn't work, until I switch:

$id === null 

to

$id !== null

.. then, everything loads as expected. What am I missing?

Here's my code:

config.php

'services' => array(
   'models' =>  array(
       'serv.widget.model.widget' => array(
             'class' => 'ServPlugin\BundleNameBundle\Model\ClassModel'
          )
   )
  ),

DefaultController.php

namespace ServPlugin\BundleNameBundle\Controller;
use Serv\CoreBundle\Controller\FormController;
use ServPlugin\BundleNameBundle\Entity\Class;

    /** @var \ServPlugin\BundleNameBundle\Model\ClassModel $classModel */
    $classModel = $this->getModel('class');
    /** @var \ServPlugin\BundleNameBundle\Entity\Class $class */
    $class = $classModel->getEntity($formId);

//html here
echo 'Total Rows: '.$class->getCount();

ClassModel.php

namespace ServPlugin\BundleNameBundleBundle\Model;
use Serv\CoreBundle\Model\FormModel;
use ServPlugin\BundleNameBundleBundle\Entity\Class;
use Symfony\Component\HttpKernel\Exception\MethodNotAllowedHttpException;

class ClassModel extends FormModel
{

public function getEntity($id = null)
{
    if ($id === null) {
        return new Class();
    }

    return parent::getEntity($id);
}

function getEntity is what I am struggling with. When I view the cache, I can see the model is loading appropriately, but I cannot access it until I go backwards on the null value.

(It turns out, $classModel is loading nothing; -- so when my code moves to $class->getCount() -- the $formId is working as it should (which is a number); the model should be loading FIRST with ServPlugin\BundleNameBundle\Model\ClassModel with ID #7, right?)

This is the error I get when I try to call it as posted above:

Call to a member function getCount() on null - in file /var/www/plugins/BundleNameBundle/Controller/DefaultController.php - at line 299 [] []

Line 299: $class->getCount()