diff --git a/core/modules/comment/src/Plugin/views/argument/UserUid.php b/core/modules/comment/src/Plugin/views/argument/UserUid.php
index aaa57d2..b9a5484 100644
--- a/core/modules/comment/src/Plugin/views/argument/UserUid.php
+++ b/core/modules/comment/src/Plugin/views/argument/UserUid.php
@@ -61,7 +61,7 @@ function title() {
     else {
       /* @var \Drupal\user\UserInterface $user */
       $user = User::load($this->argument);
-      $title = $user->getUsername();
+      $title = $user ? $user->getUsername() : NULL;
     }
     if (empty($title)) {
       return $this->t('No user');