diff -u b/core/modules/migrate_drupal/tests/src/Traits/CreateTestContentEntitiesTrait.php b/core/modules/migrate_drupal/tests/src/Traits/CreateTestContentEntitiesTrait.php
--- b/core/modules/migrate_drupal/tests/src/Traits/CreateTestContentEntitiesTrait.php
+++ b/core/modules/migrate_drupal/tests/src/Traits/CreateTestContentEntitiesTrait.php
@@ -57,45 +57,59 @@
   }
 
   /**
-   * Adds aggregator content to the created content.
+   * Create several pieces of generic content, except for feeds.
    */
   protected function createContent() {
-    // Create an aggregator feed.
+    $this->createBlockContent();
+    $this->createNode();
+    $this->createFile();
+    $this->createMenuLink();
+    $this->createTerm();
+    $this->createUser();
+  }
+
+  /**
+   * Create an aggregator feed and item.
+   */
+  protected function createFeed() {
+    $feed = Feed::create([
+      'title' => 'feed',
+      'url' => 'http://www.example.com',
+    ]);
+    $feed->save();    // Create an aggregator feed.
     $feed = Feed::create([
       'title' => 'feed',
       'url' => 'http://www.example.com',
     ]);
     $feed->save();
-
-    // Create an aggregator feed item.
     $item = Item::create([
       'title' => 'feed item',
       'fid' => $feed->id(),
       'link' => 'http://www.example.com',
     ]);
     $item->save();
-    $this->createContentUpgradeTest();
   }
 
   /**
-   * Create several pieces of generic content.
+   * Create block content.
    */
-  protected function createContentUpgradeTest() {
-    // Create a block content.
+  protected function createBlockContent() {
     $block = BlockContent::create([
       'info' => 'block',
       'type' => 'block',
     ]);
     $block->save();
+  }
 
-    // Create a node.
+  /**
+   * Create a node and comment.
+   */
+  protected function createNode() {
     $node = Node::create([
       'type' => 'page',
       'title' => 'page',
     ]);
     $node->save();
-
-    // Create a comment.
     $comment = Comment::create([
       'comment_type' => 'comment',
       'field_name' => 'comment',
@@ -103,29 +117,45 @@
       'entity_id' => $node->id(),
     ]);
     $comment->save();
+  }
 
-    // Create a file.
+  /**
+   *  Create a file.
+   */
+  protected function createFile() {
     $file = File::create([
       'uri' => 'public://example.txt',
     ]);
     $file->save();
+  }
 
-    // Create a menu link.
+  /**
+   * Create a menu link.
+   */
+  protected function createMenuLink() {
     $menu_link = MenuLinkContent::create([
       'title' => 'menu link',
       'link' => ['uri' => 'http://www.example.com'],
       'menu_name' => 'tools',
     ]);
     $menu_link->save();
+  }
 
-    // Create a taxonomy term.
+  /**
+   * Create a taxonomy term.
+   */
+  protected function createTerm() {
     $term = Term::create([
       'name' => 'term',
       'vid' => 'term',
     ]);
     $term->save();
+  }
 
-    // Create a user.
+  /**
+   * Create a user.
+   */
+  protected function createUser() {
     $user = User::create([
       'uid' => 2,
       'name' => 'user',
diff -u b/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeTestBase.php b/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeTestBase.php
--- b/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeTestBase.php
+++ b/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeTestBase.php
@@ -58,7 +58,7 @@
     $this->drupalLogin($this->rootUser);
 
     // Create content.
-    $this->createContentUpgradeTest();
+    $this->createContent();
   }
 
   /**
@@ -201,7 +201,7 @@
     \Drupal::service('module_installer')->install(['aggregator']);
 
     // Test incremental migration.
-    // Need to update available an dmissing path lists.
+    // Need to update available and missing path lists.
     $this->drupalGet('/upgrade');
     $session->responseContains('An upgrade has already been performed on this site. To perform a new migration, create a clean and empty new install of Drupal 8. Rollbacks are not yet supported through the user interface.');
     $this->drupalPostForm(NULL, [], t('Import new configuration and content from old site'));
only in patch2:
unchanged:
--- a/core/modules/aggregator/src/Plugin/Block/AggregatorFeedBlock.php
+++ b/core/modules/aggregator/src/Plugin/Block/AggregatorFeedBlock.php
@@ -167,8 +167,10 @@ public function build() {
    */
   public function getCacheTags() {
     $cache_tags = parent::getCacheTags();
-    $feed = $this->feedStorage->load($this->configuration['feed']);
-    return Cache::mergeTags($cache_tags, $feed->getCacheTags());
+    if ($feed = $this->feedStorage->load($this->configuration['feed'])) {
+      $cache_tags = Cache::mergeTags($cache_tags, $feed->getCacheTags());
+    }
+    return $cache_tags;
   }
 
 }
only in patch2:
unchanged:
--- a/core/modules/migrate_drupal/tests/src/Kernel/d6/MigrateDrupal6AuditIdsTest.php
+++ b/core/modules/migrate_drupal/tests/src/Kernel/d6/MigrateDrupal6AuditIdsTest.php
@@ -113,6 +113,7 @@ public function testAllMigrationsWithIdConflicts() {
       ->createInstancesByTag('Drupal 6');
 
     // Create content.
+    $this->createFeed();
     $this->createContent();
 
     // Audit the IDs of all migrations. There should be conflicts since content
only in patch2:
unchanged:
--- a/core/modules/migrate_drupal/tests/src/Kernel/d7/MigrateDrupal7AuditIdsTest.php
+++ b/core/modules/migrate_drupal/tests/src/Kernel/d7/MigrateDrupal7AuditIdsTest.php
@@ -112,6 +112,7 @@ public function testAllMigrationsWithIdConflicts() {
       ->createInstancesByTag('Drupal 7');
 
     // Create content.
+    $this->createFeed();
     $this->createContent();
 
     // Audit the IDs of all Drupal 7 migrations. There should be conflicts since