TypeError: Drupal\config_readonly\EventSubscriber\ReadOnlyFormSubscriber::getEditableConfigNames(): Return value must be of type array, null returned

Problem/Motivation

I'm getting an error when using this module in combination with config_readonly.

The website encountered an unexpected error. Please try again later.
TypeError: Drupal\config_readonly\EventSubscriber\ReadOnlyFormSubscriber::getEditableConfigNames(): Return value must be of type array, null returned in Drupal\config_readonly\EventSubscriber\ReadOnlyFormSubscriber->getEditableConfigNames() (line 134 of modules/contrib/config_readonly/src/EventSubscriber/ReadOnlyFormSubscriber.php).
Drupal\config_readonly\EventSubscriber\ReadOnlyFormSubscriber->getEditableConfigNames(Object) (Line: 83)
Drupal\config_readonly\EventSubscriber\ReadOnlyFormSubscriber->onFormAlter(Object, 'config_readonly_form_event', Object)
call_user_func(Array, Object, 'config_readonly_form_event', Object) (Line: 142)
Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch(Object, 'config_readonly_form_event') (Line: 21)
config_readonly_form_alter(Array, Object, 'social_virtual_event_bbb_settings_form') (Line: 562)
Drupal\Core\Extension\ModuleHandler->alter('form', Array, Object, 'social_virtual_event_bbb_settings_form') (Line: 840)
Drupal\Core\Form\FormBuilder->prepareForm('social_virtual_event_bbb_settings_form', Array, Object) (Line: 284)
Drupal\Core\Form\FormBuilder->buildForm(Object, Object) (Line: 73)
Drupal\Core\Controller\FormController->getContentResult(Object, Object)
call_user_func_array(Array, Array) (Line: 123)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 580)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 121)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array) (Line: 97)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 169)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 81)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 58)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 48)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 48)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 51)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 718)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

Steps to reproduce

Just enable config_readonly, activate read-only-mode, exclude the config for this form and hit: /admin/virtual_events/settings

Proposed resolution

Implement "getEditableConfigNames()" to return an (empty) array as the "ConfigFormBaseTrait" suggests.