Notice on previewing "default" view mode

Problem/Motivation

Previewing the "default" view mode shows PHP notices, e.g.
https://www.example.com/node/2/view-mode/preview/default
shows:

Notice: Undefined index: default in Drupal\view_modes_display\Controller\PreviewController->previewEntity() (line 95 of modules/contrib/view_modes_display/src/Controller/PreviewController.php).

    Notice: Undefined index: default in Drupal\view_modes_display\Controller\PreviewController->previewEntity() (line 95 of modules/contrib/view_modes_display/src/Controller/PreviewController.php).

    Drupal\view_modes_display\Controller\PreviewController->previewEntity(Object, 'node')
    call_user_func_array(Array, Array) (Line: 123)
    Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 564)
    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: 58)
    Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 48)
    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: 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: 709)
    Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

    Notice: Trying to access array offset on value of type null in Drupal\view_modes_display\Controller\PreviewController->previewEntity() (line 95 of modules/contrib/view_modes_display/src/Controller/PreviewController.php).

    Drupal\view_modes_display\Controller\PreviewController->previewEntity(Object, 'node')
    call_user_func_array(Array, Array) (Line: 123)
    Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 564)
    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: 58)
    Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 48)
    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: 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: 709)
    Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

Steps to reproduce

See above

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes