nullable $this->client in AbstractCrudTestCase raises PHPStan errors

[COil]

Describe the bug

Hello, I have hundred of PHPStan errors with v4.28.1 because of protected KernelBrowser $client; of  AbstractCrudTestCase which can be null now.

// final class UserCrudControllerTest extends AbstractCrudTestCase  
  public function testIndexPageException(): void
    {
        $this->client->request('GET', $this->generateIndexUrl());
>>
39     Cannot call method request() on Symfony\Bundle\FrameworkBundle\KernelBrowser|null.
         🪪  method.nonObject

To Reproduce

final class UserStepCrudControllerTest extends AbstractCrudTestCase

    public function testIndexPageException(): void
    {
        $this->client->request('GET', $this->generateIndexUrl());
        // self::getClient()->request('GET', $this->generateIndexUrl());
        self::assertResponseRedirects();
    }

PHPStan level max:

vendor/bin/phpstan analyse -c phpstan.neon --memory-limit 1G -vv

(OPTIONAL) Additional context

 39     Cannot call method request() on Symfony\Component\BrowserKit\AbstractBrowser|null.
         🪪  method.nonObject
  46     Parameter #1 $client of method App\Tests\Admin\Controller\Admin\UserStepCrudControllerTest::loginAsCOil() expects
         Symfony\Bundle\FrameworkBundle\KernelBrowser, Symfony\Component\BrowserKit\AbstractBrowser|null given.
         🪪  argument.type
  47     Cannot call method request() on Symfony\Component\BrowserKit\AbstractBrowser|null.
         🪪  method.nonObject
  54     Parameter #1 $client of method App\Tests\Admin\Controller\Admin\UserStepCrudControllerTest::loginAsCOil() expects
         Symfony\Bundle\FrameworkBundle\KernelBrowser, Symfony\Component\BrowserKit\AbstractBrowser|null given.
         🪪  argument.type
  55     Cannot call method request() on Symfony\Component\BrowserKit\AbstractBrowser|null.
         🪪  method.nonObject
  62     Parameter #1 $client of method App\Tests\Admin\Controller\Admin\UserStepCrudControllerTest::loginAsCOil() expects
         Symfony\Bundle\FrameworkBundle\KernelBrowser, Symfony\Component\BrowserKit\AbstractBrowser|null given.
         🪪  argument.type
  63     Cannot call method request() on Symfony\Component\BrowserKit\AbstractBrowser|null.
         🪪  method.nonObject
  70     Parameter #1 $client of method App\Tests\Admin\Controller\Admin\UserStepCrudControllerTest::loginAsCOil() expects
         Symfony\Bundle\FrameworkBundle\KernelBrowser, Symfony\Component\BrowserKit\AbstractBrowser|null given.
         🪪  argument.type
  71     Cannot call method request() on Symfony\Component\BrowserKit\AbstractBrowser|null.
         🪪  method.nonObject
  78     Parameter #1 $client of method App\Tests\Admin\Controller\Admin\UserStepCrudControllerTest::loginAsCOil() expects
         Symfony\Bundle\FrameworkBundle\KernelBrowser, Symfony\Component\BrowserKit\AbstractBrowser|null given.
         🪪  argument.type
  79     Cannot call method followRedirects() on Symfony\Component\BrowserKit\AbstractBrowser|null.
         🪪  method.nonObject
  80     Cannot call method request() on Symfony\Component\BrowserKit\AbstractBrowser|null.
         🪪  method.nonObject
  82     Cannot call method request() on Symfony\Component\BrowserKit\AbstractBrowser|null.
         🪪  method.nonObject
  89     Parameter #1 $client of method App\Tests\Admin\Controller\Admin\UserStepCrudControllerTest::loginAsCOil() expects
         Symfony\Bundle\FrameworkBundle\KernelBrowser, Symfony\Component\BrowserKit\AbstractBrowser|null given.
         🪪  argument.type
  90     Cannot call method followRedirects() on Symfony\Component\BrowserKit\AbstractBrowser|null.
         🪪  method.nonObject
  91     Cannot call method request() on Symfony\Component\BrowserKit\AbstractBrowser|null.
         🪪  method.nonObject
  93     Cannot call method request() on Symfony\Component\BrowserKit\AbstractBrowser|null.
         🪪  method.nonObject
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