Error with buildChallenge() function on last version 8.x-1.0-beta4

Hi!
When I visit admin/config/people/captcha/examples I get the error below.
If I back on 8.x-1.0-beta4 everything works fine.
Anyone can fix this problem?
Ty.

Notice: Undefined variable: type in Drupal\captcha\Form\CaptchaExamplesForm->buildChallenge() (line 108 of modules/contrib/captcha/src/Form/CaptchaExamplesForm.php).
Drupal\captcha\Form\CaptchaExamplesForm->buildChallenge('captcha', 'Math') (Line: 81)
Drupal\captcha\Form\CaptchaExamplesForm->buildForm(Array, Object, 'captcha', 'Math')
call_user_func_array(Array, Array) (Line: 519)
Drupal\Core\Form\FormBuilder->retrieveForm('captcha_examples', Object) (Line: 276)
Drupal\Core\Form\FormBuilder->buildForm(Object, Object) (Line: 93)
Drupal\Core\Controller\FormController->getContentResult(Object, Object)
call_user_func_array(Array, Array) (Line: 123)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 582)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 124)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array) (Line: 97)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 151)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 68)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 57)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 106)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 85)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 52)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 693)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)