diff --git a/core/tests/Drupal/Tests/Core/Template/TwigExtensionTest.php b/core/tests/Drupal/Tests/Core/Template/TwigExtensionTest.php
index 6b9525e..7ee0a59 100644
--- a/core/tests/Drupal/Tests/Core/Template/TwigExtensionTest.php
+++ b/core/tests/Drupal/Tests/Core/Template/TwigExtensionTest.php
@@ -200,6 +200,11 @@ public function testSafeJoin() {
     ];
     $result = $twig_extension->safeJoin($twig_environment, $items, '<br/>');
     $this->assertEquals('&lt;em&gt;will be escaped&lt;/em&gt;<br/><em>will be markup</em><br/><strong>will be rendered</strong>', $result);
+
+    // Ensure that safe join supports empty variables to support Twig safe mode.
+    $items = NULL;
+    $result = $twig_extension->safeJoin($twig_environment, $items, '<br>');
+    $this->assertEmpty($result);
   }
 
   /**