diff --git a/core/lib/Drupal/Core/Cache/Context/CacheContextsManager.php b/core/lib/Drupal/Core/Cache/Context/CacheContextsManager.php
index dc05e29..dde854e 100644
--- a/core/lib/Drupal/Core/Cache/Context/CacheContextsManager.php
+++ b/core/lib/Drupal/Core/Cache/Context/CacheContextsManager.php
@@ -115,10 +115,7 @@ public function convertTokensToKeys(array $context_tokens) {
         throw new \InvalidArgumentException(SafeMarkup::format('"@context" is not a valid cache context ID.', ['@context' => $context_id]));
       }
       $context = $this->getService($context_id);
-      // To make it possible to return NULL instead of CacheableMetadata.
-      if ($metadata = $context->getCacheableMetadata($parameter)) {
-        $cacheable_metadata = $cacheable_metadata->merge($metadata);
-      }
+      $cacheable_metadata = $cacheable_metadata->merge($context->getCacheableMetadata($parameter));
     }
 
     sort($optimized_tokens);
@@ -176,9 +173,15 @@ public function optimizeTokens(array $context_tokens) {
       if (strpos($context_token, '.') === FALSE && strpos($context_token, ':') === FALSE) {
         $optimized_content_tokens[] = $context_token;
       }
+      // Check cacheability. If the context defines a max-age of 0, then it
+      // can not be optimized away.
+      elseif ($this->getService($context_token)->getCacheableMetadata()->getCacheMaxAge() == 0) {
+        $optimized_content_tokens[] = $context_token;
+      }
       // The context token has a period or a colon. Iterate over all ancestor
       // cache contexts. If one exists, omit the context token.
       else {
+
         $ancestor_found = FALSE;
         // Treat a colon like a period, that allows us to consider 'a' the
         // ancestor of 'a:foo', without any additional code for the colon.
diff --git a/core/lib/Drupal/Core/Cache/Context/CookiesCacheContext.php b/core/lib/Drupal/Core/Cache/Context/CookiesCacheContext.php
index 961209d..babbd37 100644
--- a/core/lib/Drupal/Core/Cache/Context/CookiesCacheContext.php
+++ b/core/lib/Drupal/Core/Cache/Context/CookiesCacheContext.php
@@ -37,11 +37,4 @@ public function getContext($cookie = NULL) {
     }
   }
 
-  /**
-   * {@inheritdoc}
-   */
-  public function getCacheableMetadata() {
-    return NULL;
-  }
-
 }
diff --git a/core/lib/Drupal/Core/Cache/Context/HeadersCacheContext.php b/core/lib/Drupal/Core/Cache/Context/HeadersCacheContext.php
index 7cb14f2..8286b36 100644
--- a/core/lib/Drupal/Core/Cache/Context/HeadersCacheContext.php
+++ b/core/lib/Drupal/Core/Cache/Context/HeadersCacheContext.php
@@ -35,11 +35,4 @@ public function getContext($header = NULL) {
     }
   }
 
-  /**
-   * {@inheritdoc}
-   */
-  public function getCacheableMetadata($header = NULL) {
-    return NULL;
-  }
-
 }
diff --git a/core/lib/Drupal/Core/Cache/Context/IpCacheContext.php b/core/lib/Drupal/Core/Cache/Context/IpCacheContext.php
index 313806d..9cc6713 100644
--- a/core/lib/Drupal/Core/Cache/Context/IpCacheContext.php
+++ b/core/lib/Drupal/Core/Cache/Context/IpCacheContext.php
@@ -28,11 +28,4 @@ public function getContext() {
     return $this->requestStack->getCurrentRequest()->getClientIp();
   }
 
-  /**
-   * {@inheritdoc}
-   */
-  public function getCacheableMetadata() {
-    return NULL;
-  }
-
 }
diff --git a/core/lib/Drupal/Core/Cache/Context/IsSuperUserCacheContext.php b/core/lib/Drupal/Core/Cache/Context/IsSuperUserCacheContext.php
index 051b443..1f4c5ac 100644
--- a/core/lib/Drupal/Core/Cache/Context/IsSuperUserCacheContext.php
+++ b/core/lib/Drupal/Core/Cache/Context/IsSuperUserCacheContext.php
@@ -7,6 +7,8 @@
 
 namespace Drupal\Core\Cache\Context;
 
+use Drupal\Core\Cache\CacheableMetadata;
+
 /**
  * Defines the IsSuperUserCacheContext service, for "super user or not" caching.
  *
@@ -28,11 +30,4 @@ public function getContext() {
     return ((int) $this->user->id()) === 1 ? '1' : '0';
   }
 
-  /**
-   * {@inheritdoc}
-   */
-  public function getCacheableMetadata() {
-    return NULL;
-  }
-
 }
diff --git a/core/lib/Drupal/Core/Cache/Context/LanguagesCacheContext.php b/core/lib/Drupal/Core/Cache/Context/LanguagesCacheContext.php
index cdc3bad..6df0af6 100644
--- a/core/lib/Drupal/Core/Cache/Context/LanguagesCacheContext.php
+++ b/core/lib/Drupal/Core/Cache/Context/LanguagesCacheContext.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\Core\Cache\Context;
 
+use Drupal\Core\Cache\CacheableMetadata;
 use Drupal\Core\Language\LanguageManagerInterface;
 
 /**
@@ -78,7 +79,7 @@ public function getContext($type = NULL) {
    * {@inheritdoc}
    */
   public function getCacheableMetadata($type = NULL) {
-    return NULL;
+    return new CacheableMetadata();
   }
 
 }
diff --git a/core/lib/Drupal/Core/Cache/Context/MenuActiveTrailsCacheContext.php b/core/lib/Drupal/Core/Cache/Context/MenuActiveTrailsCacheContext.php
index 1b5b9c7..fc72bcb 100644
--- a/core/lib/Drupal/Core/Cache/Context/MenuActiveTrailsCacheContext.php
+++ b/core/lib/Drupal/Core/Cache/Context/MenuActiveTrailsCacheContext.php
@@ -29,6 +29,10 @@ public static function getLabel() {
    * {@inheritdoc}
    */
   public function getContext($menu_name = NULL) {
+    if (!$menu_name) {
+      throw new \InvalidArgumentException('No menu name provided for menu.active_trail cache context.');
+    }
+
     $active_trail = $this->container->get('menu.active_trail')
       ->getActiveTrailIds($menu_name);
     return 'menu_trail.' . $menu_name . '|' . implode('|', $active_trail);
@@ -38,6 +42,9 @@ public function getContext($menu_name = NULL) {
    * {@inheritdoc}
    */
   public function getCacheableMetadata($menu_name = NULL) {
+    if (!$menu_name) {
+      throw new \InvalidArgumentException('No menu name provided for menu.active_trail cache context.');
+    }
     $cacheable_metadata = new CacheableMetadata();
     return $cacheable_metadata->setCacheTags(["config:system.menu.$menu_name"]);
   }
diff --git a/core/lib/Drupal/Core/Cache/Context/PagersCacheContext.php b/core/lib/Drupal/Core/Cache/Context/PagersCacheContext.php
index 4a537dd..f53d464 100644
--- a/core/lib/Drupal/Core/Cache/Context/PagersCacheContext.php
+++ b/core/lib/Drupal/Core/Cache/Context/PagersCacheContext.php
@@ -38,11 +38,4 @@ public function getContext($pager_id = NULL) {
     return 'pager.' . $pager_id . '.' . pager_find_page($pager_id);
   }
 
-  /**
-   * {@inheritdoc}
-   */
-  public function getCacheableMetadata($pager_id = NULL) {
-    return NULL;
-  }
-
 }
diff --git a/core/lib/Drupal/Core/Cache/Context/QueryArgsCacheContext.php b/core/lib/Drupal/Core/Cache/Context/QueryArgsCacheContext.php
index f9106bd..faceb07 100644
--- a/core/lib/Drupal/Core/Cache/Context/QueryArgsCacheContext.php
+++ b/core/lib/Drupal/Core/Cache/Context/QueryArgsCacheContext.php
@@ -35,11 +35,4 @@ public function getContext($query_arg = NULL) {
     }
   }
 
-  /**
-   * {@inheritdoc}
-   */
-  public function getCacheableMetadata($query_arg = NULL) {
-    return NULL;
-  }
-
 }
diff --git a/core/lib/Drupal/Core/Cache/Context/RequestStackCacheContextBase.php b/core/lib/Drupal/Core/Cache/Context/RequestStackCacheContextBase.php
index 9909399..f4c960f 100644
--- a/core/lib/Drupal/Core/Cache/Context/RequestStackCacheContextBase.php
+++ b/core/lib/Drupal/Core/Cache/Context/RequestStackCacheContextBase.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\Core\Cache\Context;
 
+use Drupal\Core\Cache\CacheableMetadata;
 use Symfony\Component\HttpFoundation\RequestStack;
 
 /**
@@ -35,7 +36,7 @@ public function __construct(RequestStack $request_stack) {
    * {@inheritdoc}
    */
   public function getCacheableMetadata() {
-    return NULL;
+    return new CacheableMetadata();
   }
 
 }
diff --git a/core/lib/Drupal/Core/Cache/Context/RouteCacheContext.php b/core/lib/Drupal/Core/Cache/Context/RouteCacheContext.php
index 3059a44..4b4f21b 100644
--- a/core/lib/Drupal/Core/Cache/Context/RouteCacheContext.php
+++ b/core/lib/Drupal/Core/Cache/Context/RouteCacheContext.php
@@ -52,7 +52,7 @@ public function getContext() {
    * {@inheritdoc}
    */
   public function getCacheableMetadata() {
-    return NULL;
+    return new CacheableMetadata();
   }
 
 }
diff --git a/core/lib/Drupal/Core/Cache/Context/ThemeCacheContext.php b/core/lib/Drupal/Core/Cache/Context/ThemeCacheContext.php
index 46ff397..7e451af 100644
--- a/core/lib/Drupal/Core/Cache/Context/ThemeCacheContext.php
+++ b/core/lib/Drupal/Core/Cache/Context/ThemeCacheContext.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\Core\Cache\Context;
 
+use Drupal\Core\Cache\CacheableMetadata;
 use Drupal\Core\Theme\ThemeManagerInterface;
 
 /**
@@ -51,7 +52,7 @@ public function getContext() {
    * {@inheritdoc}
    */
   public function getCacheableMetadata() {
-    return NULL;
+    return new CacheableMetadata();
   }
 
 }
diff --git a/core/lib/Drupal/Core/Cache/Context/TimeZoneCacheContext.php b/core/lib/Drupal/Core/Cache/Context/TimeZoneCacheContext.php
index 84321ce..71dab96 100644
--- a/core/lib/Drupal/Core/Cache/Context/TimeZoneCacheContext.php
+++ b/core/lib/Drupal/Core/Cache/Context/TimeZoneCacheContext.php
@@ -7,6 +7,8 @@
 
 namespace Drupal\Core\Cache\Context;
 
+use Drupal\Core\Cache\CacheableMetadata;
+
 /**
  * Defines the TimeZoneCacheContext service, for "per time zone" caching.
  *
@@ -36,7 +38,7 @@ public function getContext() {
    * {@inheritdoc}
    */
   public function getCacheableMetadata() {
-    return NULL;
+    return new CacheableMetadata();
   }
 
 }
diff --git a/core/lib/Drupal/Core/Cache/Context/UserCacheContext.php b/core/lib/Drupal/Core/Cache/Context/UserCacheContext.php
index 5ed0c1e..983f8a3 100644
--- a/core/lib/Drupal/Core/Cache/Context/UserCacheContext.php
+++ b/core/lib/Drupal/Core/Cache/Context/UserCacheContext.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\Core\Cache\Context;
 
+use Drupal\Core\Cache\CacheableMetadata;
 use Drupal\Core\Session\AccountInterface;
 
 /**
@@ -44,7 +45,7 @@ public function getContext() {
    * {@inheritdoc}
    */
   public function getCacheableMetadata() {
-    return NULL;
+    return new CacheableMetadata();
   }
 
 }
diff --git a/core/lib/Drupal/Core/Cache/Context/UserRolesCacheContext.php b/core/lib/Drupal/Core/Cache/Context/UserRolesCacheContext.php
index eed0d01..4221f14 100644
--- a/core/lib/Drupal/Core/Cache/Context/UserRolesCacheContext.php
+++ b/core/lib/Drupal/Core/Cache/Context/UserRolesCacheContext.php
@@ -45,11 +45,4 @@ public function getContext($role = NULL) {
     }
   }
 
-  /**
-   * {@inheritdoc}
-   */
-  public function getCacheableMetadata($role = NULL) {
-    return NULL;
-  }
-
 }
diff --git a/core/modules/comment/src/Tests/CommentRssTest.php b/core/modules/comment/src/Tests/CommentRssTest.php
index 93c0282..aed6be8 100644
--- a/core/modules/comment/src/Tests/CommentRssTest.php
+++ b/core/modules/comment/src/Tests/CommentRssTest.php
@@ -53,6 +53,15 @@ function testCommentRss() {
     $this->postComment($this->node, $this->randomMachineName(), $this->randomMachineName());
     $this->drupalGet('rss.xml');
 
+    $cache_contexts = [
+      'languages:language_interface',
+      'theme',
+      'user.node_grants:view',
+      'user.permissions',
+      'timezone',
+    ];
+    $this->assertCacheContexts($cache_contexts);
+
     $cache_context_tags = \Drupal::service('cache_contexts_manager')->convertTokensToKeys($cache_contexts)->getCacheableMetadata()->getCacheTags();
     $this->assertCacheTags(Cache::mergeTags($cache_context_tags, [
       'config:views.view.frontpage',
@@ -61,14 +70,6 @@ function testCommentRss() {
       'user:3',
     ]));
 
-    $this->assertCacheContexts([
-      'languages:language_interface',
-      'theme',
-      'user.node_grants:view',
-      'user.permissions',
-      'timezone',
-    ]);
-
     $raw = '<comments>' . $this->node->url('canonical', array('fragment' => 'comments', 'absolute' => TRUE)) . '</comments>';
     $this->assertRaw($raw, 'Comments as part of RSS feed.');
 
diff --git a/core/modules/node/src/Cache/NodeAccessGrantsCacheContext.php b/core/modules/node/src/Cache/NodeAccessGrantsCacheContext.php
index 8f64cbe..10c09f4 100644
--- a/core/modules/node/src/Cache/NodeAccessGrantsCacheContext.php
+++ b/core/modules/node/src/Cache/NodeAccessGrantsCacheContext.php
@@ -87,7 +87,15 @@ protected function checkNodeGrants($operation) {
    * {@inheritdoc}
    */
   public function getCacheableMetadata($operation = NULL) {
-    return NULL;
+    $cacheable_metadata = new CacheableMetadata();
+
+    if (!\Drupal::moduleHandler()->getImplementations('node_grants')) {
+      return $cacheable_metadata;
+    }
+
+    // If the site is using node grants, this cache context can not be
+    // optimized.
+    return $cacheable_metadata->setCacheMaxAge(0);
   }
 
 }
diff --git a/core/modules/system/tests/modules/entity_test/src/Cache/EntityTestViewGrantsCacheContext.php b/core/modules/system/tests/modules/entity_test/src/Cache/EntityTestViewGrantsCacheContext.php
index f2e3bb2..9d49470 100644
--- a/core/modules/system/tests/modules/entity_test/src/Cache/EntityTestViewGrantsCacheContext.php
+++ b/core/modules/system/tests/modules/entity_test/src/Cache/EntityTestViewGrantsCacheContext.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\entity_test\Cache;
 
+use Drupal\Core\Cache\CacheableMetadata;
 use Drupal\Core\Cache\Context\CacheContextInterface;
 
 /**
@@ -38,7 +39,7 @@ public function getContext() {
    * {@inheritdoc}
    */
   public function getCacheableMetadata() {
-    return NULL;
+    return new CacheableMetadata();
   }
 
 }
diff --git a/core/modules/views/tests/modules/views_test_data/src/Cache/ViewsTestCacheContext.php b/core/modules/views/tests/modules/views_test_data/src/Cache/ViewsTestCacheContext.php
index 88d7559..e9ddc08 100644
--- a/core/modules/views/tests/modules/views_test_data/src/Cache/ViewsTestCacheContext.php
+++ b/core/modules/views/tests/modules/views_test_data/src/Cache/ViewsTestCacheContext.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\views_test_data\Cache;
 
+use Drupal\Core\Cache\CacheableMetadata;
 use Drupal\Core\Cache\Context\CacheContextInterface;
 
 /**
@@ -34,7 +35,7 @@ public function getContext() {
    * {@inheritdoc}
    */
   public function getCacheableMetadata() {
-    return NULL;
+    return new CacheableMetadata();
   }
 
 }
diff --git a/core/tests/Drupal/Tests/Core/Cache/Context/CacheContextsManagerTest.php b/core/tests/Drupal/Tests/Core/Cache/Context/CacheContextsManagerTest.php
index c6c06a5..818aec4 100644
--- a/core/tests/Drupal/Tests/Core/Cache/Context/CacheContextsManagerTest.php
+++ b/core/tests/Drupal/Tests/Core/Cache/Context/CacheContextsManagerTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\Tests\Core\Cache\Context;
 
+use Drupal\Core\Cache\CacheableMetadata;
 use Drupal\Core\Cache\Context\CacheContextsManager;
 use Drupal\Core\Cache\Context\CacheContextInterface;
 use Drupal\Core\Cache\Context\CalculatedCacheContextInterface;
@@ -238,7 +239,7 @@ public function getContext() {
    * {@inheritdoc}
    */
   public function getCacheableMetadata() {
-    return NULL;
+    return new CacheableMetadata();
   }
 
 }
@@ -269,7 +270,7 @@ public function getContext($parameter = NULL) {
    * {@inheritdoc}
    */
   public function getCacheableMetadata($parameter = NULL) {
-    return NULL;
+    return new CacheableMetadata();
   }
 
 }