PHP 8.1: do not pass null to Html::escape() and Unicode::truncate().

Problem/Motivation

Using Drupal 9.3.6 and upgraded from PHP 7.4 to PHP 8.1

Now I get the following error:

Deprecated function: htmlspecialchars(): Passing null to parameter #1 ($string) of type string is deprecated in Drupal\Component\Utility\Html::escape() (line 424 of core/lib/Drupal/Component/Utility/Html.php).
Drupal\Component\Utility\Html::escape(NULL) (Line: 125)
Drupal\feeds\Controller\ItemListController->listItems(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: 317)
Drupal\cleantalk\EventSubscriber\BootSubscriber->handle(Object, 1, 1) (Line: 49)
Asm89\Stack\Cors->handle(Object, 1, 1) (Line: 57)
Drupal\advban\AdvbanMiddleware->handle(Object, 1, 1) (Line: 50)
Drupal\ban\BanMiddleware->handle(Object, 1, 1) (Line: 265)
Drupal\shield\ShieldMiddleware->bypass(Object, 1, 1) (Line: 221)
Drupal\shield\ShieldMiddleware->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)