Undefined index: target_bundles

Notice: Undefined index: target_bundles in Drupal\inline_entity_form\Plugin\Field\FieldWidget\InlineEntityFormSimple::isApplicable() (line 157 of modules/contrib/inline_entity_form/src/Plugin/Field/FieldWidget/InlineEntityFormSimple.php).
Drupal\inline_entity_form\Plugin\Field\FieldWidget\InlineEntityFormSimple::isApplicable(Object)
Drupal\field_ui\Form\EntityDisplayFormBase->getPluginOptions(Object)
Drupal\field_ui\Form\EntityDisplayFormBase->buildFieldRow(Object, Array, Object)
Drupal\field_ui\Form\EntityFormDisplayEditForm->buildFieldRow(Object, Array, Object)
Drupal\field_ui\Form\EntityDisplayFormBase->form(Array, Object)
Drupal\Core\Entity\EntityForm->buildForm(Array, Object)
call_user_func_array(Array, Array)
Drupal\Core\Form\FormBuilder->retrieveForm('entity_form_display_edit_form', Object)
Drupal\Core\Form\FormBuilder->buildForm(Object, Object)
Drupal\Core\Controller\FormController->getContentResult(Object, Object)
call_user_func_array(Array, Array)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}()
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}()
call_user_func_array(Object, Array)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1)
Stack\StackedHttpKernel->handle(Object, 1, 1)
Drupal\Core\DrupalKernel->handle(Object)

Happens when you have an entity without a bundle (so no target_bundles?).