Error: Call to undefined method Drupal\simplenews\Subscription\SubscriptionManager::()

Problem/Motivation

I have upgraded from version 8.x-1.5 to 8.x-1.6 and when submitting a form with the webform_simplenews handler enabled i get the following error:

Error: Call to undefined method Drupal\simplenews\Subscription\SubscriptionManager::() in Drupal\webform_simplenews_handler\Plugin\WebformHandler\SubmissionSimplenewsWebformHandler->postSave() (line 375 of C:\wamp64\www\dasta\web\modules\contrib\webform_simplenews_handler\src\Plugin\WebformHandler\SubmissionSimplenewsWebformHandler.php)

#0 C:\wamp64\www\dasta\web\modules\contrib\webform\src\Entity\Webform.php(2751): Drupal\webform_simplenews_handler\Plugin\WebformHandler\SubmissionSimplenewsWebformHandler->postSave(Object(Drupal\webform\Entity\WebformSubmission), false, NULL)
#1 C:\wamp64\www\dasta\web\modules\contrib\webform\src\WebformSubmissionStorage.php(1213): Drupal\webform\Entity\Webform->invokeHandlers('postSave', Object(Drupal\webform\Entity\WebformSubmission), false, NULL)
#2 C:\wamp64\www\dasta\web\modules\contrib\webform\src\WebformSubmissionStorage.php(1121): Drupal\webform\WebformSubmissionStorage->invokeWebformHandlers('postSave', Object(Drupal\webform\Entity\WebformSubmission), false)
#3 C:\wamp64\www\dasta\web\core\lib\Drupal\Core\Entity\EntityStorageBase.php(523): Drupal\webform\WebformSubmissionStorage->doPostSave(Object(Drupal\webform\Entity\WebformSubmission), false)
#4 C:\wamp64\www\dasta\web\core\lib\Drupal\Core\Entity\Sql\SqlContentEntityStorage.php(804): Drupal\Core\Entity\EntityStorageBase->save(Object(Drupal\webform\Entity\WebformSubmission))
#5 C:\wamp64\www\dasta\web\modules\contrib\webform\src\WebformSubmissionStorage.php(984): Drupal\Core\Entity\Sql\SqlContentEntityStorage->save(Object(Drupal\webform\Entity\WebformSubmission))
#6 C:\wamp64\www\dasta\web\core\lib\Drupal\Core\Entity\EntityBase.php(339): Drupal\webform\WebformSubmissionStorage->save(Object(Drupal\webform\Entity\WebformSubmission))
#7 C:\wamp64\www\dasta\web\modules\contrib\webform\src\Entity\WebformSubmission.php(887): Drupal\Core\Entity\EntityBase->save()
#8 C:\wamp64\www\dasta\web\modules\contrib\webform\src\WebformSubmissionForm.php(1972): Drupal\webform\Entity\WebformSubmission->save()
#9 [internal function]: Drupal\webform\WebformSubmissionForm->save(Array, Object(Drupal\Core\Form\FormState))
#10 C:\wamp64\www\dasta\web\core\lib\Drupal\Core\Form\FormSubmitter.php(114): call_user_func_array(Array, Array)
#11 C:\wamp64\www\dasta\web\core\lib\Drupal\Core\Form\FormSubmitter.php(52): Drupal\Core\Form\FormSubmitter->executeSubmitHandlers(Array, Object(Drupal\Core\Form\FormState))
#12 C:\wamp64\www\dasta\web\core\lib\Drupal\Core\Form\FormBuilder.php(592): Drupal\Core\Form\FormSubmitter->doSubmitForm(Array, Object(Drupal\Core\Form\FormState))
#13 C:\wamp64\www\dasta\web\core\lib\Drupal\Core\Form\FormBuilder.php(320): Drupal\Core\Form\FormBuilder->processForm('webform_submiss...', Array, Object(Drupal\Core\Form\FormState))
#14 C:\wamp64\www\dasta\web\core\lib\Drupal\Core\Entity\EntityFormBuilder.php(48): Drupal\Core\Form\FormBuilder->buildForm(Object(Drupal\webform\WebformSubmissionForm), Object(Drupal\Core\Form\FormState))
#15 C:\wamp64\www\dasta\web\modules\contrib\webform\src\Entity\Webform.php(1243): Drupal\Core\Entity\EntityFormBuilder->getForm(Object(Drupal\webform\Entity\WebformSubmission), 'add')
#16 C:\wamp64\www\dasta\web\modules\contrib\webform\src\Controller\WebformEntityController.php(76): Drupal\webform\Entity\Webform->getSubmissionForm()
#17 [internal function]: Drupal\webform\Controller\WebformEntityController->addForm(Object(Symfony\Component\HttpFoundation\Request), Object(Drupal\webform\Entity\Webform))
#18 C:\wamp64\www\dasta\web\core\lib\Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber.php(123): call_user_func_array(Array, Array)
#19 C:\wamp64\www\dasta\web\core\lib\Drupal\Core\Render\Renderer.php(564): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}()
#20 C:\wamp64\www\dasta\web\core\lib\Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber.php(124): Drupal\Core\Render\Renderer->executeInRenderContext(Object(Drupal\Core\Render\RenderContext), Object(Closure))
#21 C:\wamp64\www\dasta\web\core\lib\Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber.php(97): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array)
#22 C:\wamp64\www\dasta\vendor\symfony\http-kernel\HttpKernel.php(169): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}()
#23 C:\wamp64\www\dasta\vendor\symfony\http-kernel\HttpKernel.php(81): Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object(Symfony\Component\HttpFoundation\Request), 1)
#24 C:\wamp64\www\dasta\web\core\lib\Drupal\Core\StackMiddleware\Session.php(58): Symfony\Component\HttpKernel\HttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#25 C:\wamp64\www\dasta\web\core\lib\Drupal\Core\StackMiddleware\KernelPreHandle.php(48): Drupal\Core\StackMiddleware\Session->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#26 C:\wamp64\www\dasta\web\core\modules\page_cache\src\StackMiddleware\PageCache.php(106): Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#27 C:\wamp64\www\dasta\web\core\modules\page_cache\src\StackMiddleware\PageCache.php(85): Drupal\page_cache\StackMiddleware\PageCache->pass(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#28 C:\wamp64\www\dasta\web\core\lib\Drupal\Core\StackMiddleware\ReverseProxyMiddleware.php(48): Drupal\page_cache\StackMiddleware\PageCache->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#29 C:\wamp64\www\dasta\web\core\lib\Drupal\Core\StackMiddleware\NegotiationMiddleware.php(51): Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#30 C:\wamp64\www\dasta\vendor\stack\builder\src\Stack\StackedHttpKernel.php(23): Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#31 C:\wamp64\www\dasta\web\core\lib\Drupal\Core\DrupalKernel.php(709): Stack\StackedHttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#32 C:\wamp64\www\dasta\web\index.php(19): Drupal\Core\DrupalKernel->handle(Object(Symfony\Component\HttpFoundation\Request))
#33 {main}

I use Drupal core version 9.4.9 and simplenews version 3.0.0-beta4.

It seems that compared to version 8.x-1.5 there is a change in src\Plugin\WebformHandler\SubmissionSimplenewsWebformHandler.php from:

$this->subscriptionManager->subscribe($email_value, $newsletter_id, NULL, 'website');

to:

$action = $this->configuration['action'];
$this->subscriptionManager->$action($email_value, $newsletter_id, NULL, 'website');

The problem is that $this->configuration['action'] is empty for existing handlers. If I update the handler from the UI, the configuration value is saved and the handler works without errors.

As a temporary solution one should visit all webform_simplenews handlers and save their settings choosing either subscribe or unsubscribe as the action. However, the module should handle the case of existing handlers when updating.