PHP warnings when submitting a contact form with empty message

Problem/Motivation

Since I updated the module to 6.1.0, I'm getting PHP warnings in the log when someone submits a contact form with empty Message.

Steps to reproduce:

- install with standard profile
- enable webform, disable_html5_validation, captcha modules
- /admin/structure/webform/manage/contact, set the "Elements (YAML)" to this:

container:
  '#type': container
  '#attributes':
    class:
      - form-border
  name:
    '#title': 'Your Name'
    '#type': textfield
    '#required': true
    '#default_value': '[current-user:display-name]'
  phone:
    '#type': textfield
    '#title': Phone
  email:
    '#title': 'Your Email'
    '#type': email
    '#required': true
    '#default_value': '[current-user:mail]'
  message:
    '#title': Message
    '#type': textarea
    '#required': true
    '#test': 'Please ignore this email.'
  captcha:
    '#type': captcha
  actions:
    '#type': webform_actions
    '#title': 'Submit button(s)'
    '#submit__label': 'Send message'
    '#submit__attributes':
      class:
        - cta

- /admin/config/people/captcha tick "Add CAPTCHA administration links to forms"
- visit /webform/contact as admin and click to "Send message" with empty message.
- the PHP warning should be logged in /admin/reports/dblog

Error messages:

Notice: Undefined index: #parents in Drupal\Core\Form\FormState->getError() (line 1112 of core/lib/Drupal/Core/Form/FormState.php).
Drupal\Core\Form\FormState->getError(Array) (Line: 164)
Drupal\Core\Form\FormErrorHandler->setElementErrorsFromFormState(Array, Object, Array) (Line: 124)
Drupal\Core\Form\FormErrorHandler->setElementErrorsFromFormState(Array, Object, Array) (Line: 124)
Drupal\Core\Form\FormErrorHandler->setElementErrorsFromFormState(Array, Object) (Line: 26)
Drupal\Core\Form\FormErrorHandler->handleFormErrors(Array, Object) (Line: 199)
Drupal\Core\Form\FormValidator->finalizeValidation(Array, Object, 'webform_submission_contact_add_form') (Line: 119)
Drupal\Core\Form\FormValidator->validateForm('webform_submission_contact_add_form', Array, Object) (Line: 589)
Drupal\Core\Form\FormBuilder->processForm('webform_submission_contact_add_form', Array, Object) (Line: 321)
Drupal\Core\Form\FormBuilder->buildForm(Object, Object) (Line: 48)
Drupal\Core\Entity\EntityFormBuilder->getForm(Object, 'add') (Line: 1233)
Drupal\webform\Entity\Webform->getSubmissionForm() (Line: 76)
Drupal\webform\Controller\WebformEntityController->addForm(Object, Object)
call_user_func_array(Array, Array) (Line: 123)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 578)
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: 158)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 80)
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: 717)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)


Warning: Invalid argument supplied for foreach() in Drupal\Core\Form\FormState->getError() (line 1112 of core/lib/Drupal/Core/Form/FormState.php).
Drupal\Core\Form\FormState->getError(Array) (Line: 164)
Drupal\Core\Form\FormErrorHandler->setElementErrorsFromFormState(Array, Object, Array) (Line: 124)
Drupal\Core\Form\FormErrorHandler->setElementErrorsFromFormState(Array, Object, Array) (Line: 124)
Drupal\Core\Form\FormErrorHandler->setElementErrorsFromFormState(Array, Object) (Line: 26)
Drupal\Core\Form\FormErrorHandler->handleFormErrors(Array, Object) (Line: 199)
Drupal\Core\Form\FormValidator->finalizeValidation(Array, Object, 'webform_submission_contact_add_form') (Line: 119)
Drupal\Core\Form\FormValidator->validateForm('webform_submission_contact_add_form', Array, Object) (Line: 589)
Drupal\Core\Form\FormBuilder->processForm('webform_submission_contact_add_form', Array, Object) (Line: 321)
Drupal\Core\Form\FormBuilder->buildForm(Object, Object) (Line: 48)
Drupal\Core\Entity\EntityFormBuilder->getForm(Object, 'add') (Line: 1233)
Drupal\webform\Entity\Webform->getSubmissionForm() (Line: 76)
Drupal\webform\Controller\WebformEntityController->addForm(Object, Object)
call_user_func_array(Array, Array) (Line: 123)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 578)
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: 158)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 80)
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: 717)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes