Warning: Invalid argument supplied for foreach()

Whenever a webform is opened a PHP warning is generated:

Warning: Invalid argument supplied for foreach() in Drupal\webform\WebformSubmissionForm->getWebformSetting() (line 1569 of /var/www/docroot/modules/contrib/webform/src/WebformSubmissionForm.php) #0 /var/www/docroot/core/includes/bootstrap.inc(548): _drupal_error_handler_real(2, 'Invalid argumen...', '/var/www/docroo...', 1569, Array) #1 /var/www/docroot/modules/contrib/webform/src/WebformSubmissionForm.php(1569): _drupal_error_handler(2, 'Invalid argumen...', '/var/www/docroo...', 1569, Array) #2 /var/www/docroot/modules/contrib/webform/src/WebformSubmissionForm.php(522): Drupal\webform\WebformSubmissionForm->getWebformSetting('form_previous_s...', false) #3 /var/www/docroot/modules/contrib/webform/src/WebformSubmissionForm.php(216): Drupal\webform\WebformSubmissionForm->displayMessages(Array, Object(Drupal\Core\Form\FormState)) #4 [internal function]: Drupal\webform\WebformSubmissionForm->buildForm(Array, Object(Drupal\Core\Form\FormState)) #5 /var/www/docroot/core/lib/Drupal/Core/Form/FormBuilder.php(514): call_user_func_array(Array, Array) #6 /var/www/docroot/core/lib/Drupal/Core/Form/FormBuilder.php(271): Drupal\Core\Form\FormBuilder->retrieveForm('webform_submiss...', Object(Drupal\Core\Form\FormState)) #7 /var/www/docroot/core/lib/Drupal/Core/Entity/EntityFormBuilder.php(48): Drupal\Core\Form\FormBuilder->buildForm(Object(Drupal\webform\WebformSubmissionForm), Object(Drupal\Core\Form\FormState)) #8 /var/www/docroot/modules/contrib/webform/src/Entity/Webform.php(808): Drupal\Core\Entity\EntityFormBuilder->getForm(Object(Drupal\webform\Entity\WebformSubmission), 'default') #9 /var/www/docroot/modules/contrib/webform/src/Controller/WebformController.php(82): Drupal\webform\Entity\Webform->getSubmissionForm() #10 [internal function]: Drupal\webform\Controller\WebformController->addForm(Object(Symfony\Component\HttpFoundation\Request), Object(Drupal\webform\Entity\Webform)) #11 /var/www/docroot/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(123): call_user_func_array(Array, Array) #12 /var/www/docroot/core/lib/Drupal/Core/Render/Renderer.php(574): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() #13 /var/www/docroot/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(124): Drupal\Core\Render\Renderer->executeInRenderContext(Object(Drupal\Core\Render\RenderContext), Object(Closure)) #14 /var/www/docroot/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php(97): Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array) #15 [internal function]: Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() #16 /var/www/vendor/symfony/http-kernel/HttpKernel.php(144): call_user_func_array(Object(Closure), Array) #17 /var/www/vendor/symfony/http-kernel/HttpKernel.php(64): Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object(Symfony\Component\HttpFoundation\Request), 1) #18 /var/www/docroot/core/lib/Drupal/Core/StackMiddleware/Session.php(57): Symfony\Component\HttpKernel\HttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #19 /var/www/docroot/core/lib/Drupal/Core/StackMiddleware/KernelPreHandle.php(47): Drupal\Core\StackMiddleware\Session->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #20 /var/www/docroot/modules/contrib/shield/src/ShieldMiddleware.php(68): Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #21 /var/www/docroot/core/lib/Drupal/Core/StackMiddleware/ReverseProxyMiddleware.php(47): Drupal\shield\ShieldMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #22 /var/www/docroot/core/lib/Drupal/Core/StackMiddleware/NegotiationMiddleware.php(50): Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #23 /var/www/vendor/stack/builder/src/Stack/StackedHttpKernel.php(23): Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #24 /var/www/docroot/core/lib/Drupal/Core/DrupalKernel.php(652): Stack\StackedHttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #25 /var/www/docroot/index.php(19): Drupal\Core\DrupalKernel->handle(Object(Symfony\Component\HttpFoundation\Request)) #26 {main}.

Other than the warning webforms seems to work without any problem.
Problem is reproducible on D8.2.7 for any new or previously created webform.