diff --git a/core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php
index 4493612..67ae505 100644
--- a/core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/FinishResponseSubscriber.php
@@ -177,18 +177,22 @@ public function onRespond(FilterResponseEvent $event) {
    */
   protected function updateDrupalCacheHeaders(Response $response, array $cache_tags = [], array $cache_contexts = []) {
     // X-Drupal-Cache-Tags
-    if ($response->headers->has('X-Drupal-Cache-Tags')) {
-      $existing_cache_tags = explode(' ', $response->headers->get('X-Drupal-Cache-Tags'));
-      $cache_tags = Cache::mergeTags($existing_cache_tags, $cache_tags);
+    if ($cache_tags) {
+      if ($response->headers->has('X-Drupal-Cache-Tags')) {
+        $existing_cache_tags = explode(' ', $response->headers->get('X-Drupal-Cache-Tags'));
+        $cache_tags = Cache::mergeTags($existing_cache_tags, $cache_tags);
+      }
+      $response->headers->set('X-Drupal-Cache-Tags', implode(' ', $cache_tags));
     }
-    $response->headers->set('X-Drupal-Cache-Tags', implode(' ', $cache_tags));
 
     // X-Drupal-Cache-Contexts
-    if ($response->headers->has('X-Drupal-Cache-Contexts')) {
-      $existing_cache_contexts = explode(' ', $response->headers->get('X-Drupal-Cache-Contexts'));
-      $cache_contexts = Cache::mergeContexts($existing_cache_contexts, $cache_contexts);
+    if ($cache_contexts) {
+      if ($response->headers->has('X-Drupal-Cache-Contexts')) {
+        $existing_cache_contexts = explode(' ', $response->headers->get('X-Drupal-Cache-Contexts'));
+        $cache_contexts = Cache::mergeContexts($existing_cache_contexts, $cache_contexts);
+      }
+      $response->headers->set('X-Drupal-Cache-Contexts', implode(' ', $this->cacheContexts->optimizeTokens($cache_contexts)));
     }
-    $response->headers->set('X-Drupal-Cache-Contexts', implode(' ', $this->cacheContexts->optimizeTokens($cache_contexts)));
   }
 
   /**
diff --git a/core/modules/system/src/Tests/Routing/RouterTest.php b/core/modules/system/src/Tests/Routing/RouterTest.php
index e0a4f34..b567f28 100644
--- a/core/modules/system/src/Tests/Routing/RouterTest.php
+++ b/core/modules/system/src/Tests/Routing/RouterTest.php
@@ -71,13 +71,13 @@ public function testFinishResponseSubscriber() {
     // 3. controller result: Response object, globally cacheable route access.
     $this->drupalGet('router_test/test1');
     $headers = $this->drupalGetHeaders();
-    $this->assertEqual($headers['x-drupal-cache-contexts'], '');
-    $this->assertEqual($headers['x-drupal-cache-tags'], '');
+    $this->assertTrue(!isset($headers['x-drupal-cache-contexts']));
+    $this->assertTrue(!isset($headers['x-drupal-cache-tags']));
     // 4. controller result: Response object, per-role cacheable route access.
     $this->drupalGet('router_test/test20');
     $headers = $this->drupalGetHeaders();
     $this->assertEqual($headers['x-drupal-cache-contexts'], 'user.roles');
-    $this->assertEqual($headers['x-drupal-cache-tags'], '');
+    $this->assertTrue(!isset($headers['x-drupal-cache-tags']));
   }
 
   /**