Notice on form display

Problem/Motivation

On manage form display following notice is displayed.

Notice: Undefined variable: targets_available in Drupal\link_target\Plugin\Field\FieldWidget\LinkTargetFieldWidget->getSelectedOptions() (line 141 of modules/contrib/link_target/src/Plugin/Field/FieldWidget/LinkTargetFieldWidget.php).
Drupal\link_target\Plugin\Field\FieldWidget\LinkTargetFieldWidget->getSelectedOptions() (Line: 53)
Drupal\link_target\Plugin\Field\FieldWidget\LinkTargetFieldWidget->settingsSummary() (Line: 431)
Drupal\field_ui\Form\EntityDisplayFormBase->buildFieldRow(Object, Array, Object) (Line: 40)
Drupal\field_ui\Form\EntityFormDisplayEditForm->buildFieldRow(Object, Array, Object) (Line: 209)
Drupal\field_ui\Form\EntityDisplayFormBase->form(Array, Object) (Line: 106)
Drupal\Core\Entity\EntityForm->buildForm(Array, Object)
call_user_func_array(Array, Array) (Line: 531)
Drupal\Core\Form\FormBuilder->retrieveForm('entity_form_display_edit_form', Object) (Line: 278)
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: 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: 708)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)