Function maxlength_field_widget_third_party_settings_form() should return array, not null

Working on it!!

Yes i agree that if there is nothing to show then also it should return an array, thus made the required changes.
Please review!!

The patch is straightforward and very needed.

Marking as major because it can cause a fatal error when you try to go to the manage display form of a content type (for example /admin/structure/types/manage/article/form-display). And there is no easy way to figure out that maxlength is to blame without a debugger (or searching the web now that i'm dumping the entire error message here):

The website encountered an unexpected error. Try again later.

TypeError: Unsupported operand types: array + null in Drupal\field_ui\Form\EntityFormDisplayEditForm->{closure:Drupal\field_ui\Form\EntityFormDisplayEditForm::thirdPartySettingsForm():129}() (line 131 of core/modules/field_ui/src/Form/EntityFormDisplayEditForm.php).

And the stacktrace:

Drupal\Core\Extension\ModuleHandler->invokeAllWith() (Line: 127)
Drupal\field_ui\Form\EntityFormDisplayEditForm->thirdPartySettingsForm() (Line: 459)
Drupal\field_ui\Form\EntityDisplayFormBase->buildFieldRow() (Line: 40)
Drupal\field_ui\Form\EntityFormDisplayEditForm->buildFieldRow() (Line: 213)
Drupal\field_ui\Form\EntityDisplayFormBase->form() (Line: 107)
Drupal\Core\Entity\EntityForm->buildForm()
call_user_func_array() (Line: 528)
Drupal\Core\Form\FormBuilder->retrieveForm() (Line: 279)
Drupal\Core\Form\FormBuilder->buildForm() (Line: 73)
Drupal\Core\Controller\FormController->getContentResult()
call_user_func_array() (Line: 123)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->{closure:Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber::wrapControllerExecutionInRenderContext():121}() (Line: 622)
Drupal\Core\Render\Renderer->executeInRenderContext() (Line: 121)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext() (Line: 97)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->{closure:Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber::onController():96}() (Line: 183)
Symfony\Component\HttpKernel\HttpKernel->handleRaw() (Line: 76)
Symfony\Component\HttpKernel\HttpKernel->handle() (Line: 53)
Drupal\Core\StackMiddleware\Session->handle() (Line: 48)
Drupal\Core\StackMiddleware\KernelPreHandle->handle() (Line: 28)
Drupal\Core\StackMiddleware\ContentLength->handle() (Line: 32)
Drupal\big_pipe\StackMiddleware\ContentLength->handle() (Line: 116)
Drupal\page_cache\StackMiddleware\PageCache->pass() (Line: 90)
Drupal\page_cache\StackMiddleware\PageCache->handle() (Line: 48)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle() (Line: 51)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle() (Line: 53)
Drupal\Core\StackMiddleware\AjaxPageState->handle() (Line: 51)
Drupal\Core\StackMiddleware\StackedHttpKernel->handle() (Line: 715)
Drupal\Core\DrupalKernel->handle() (Line: 19)

Thank you for the report and the fix!