Issue #3202014 by mondrake, daffie: pager_test_preprocess_pager() should...

Issue #3202014 by mondrake, daffie: pager_test_preprocess_pager() should return if pager element is not defined

core/modules/system/tests/modules/pager_test/pager_test.module

@@ -14,6 +14,13 @@ function pager_test_preprocess_pager(&$variables) {
   /** @var \Drupal\Core\Pager\PagerManagerInterface $pager_manager */
   $pager_manager = \Drupal::service('pager.manager');
   $pager = $pager_manager->getPager($element);
+
+  // Nothing to do if there is no pager.
+  if (!isset($pager)) {
+    return;
+  }
+
+  // Nothing to do if there is only one page.
   if ($pager->getTotalPages() <= 1) {
     return;
   }