diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index b4b64474a6..75311c488e 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -1153,7 +1153,7 @@ function template_preprocess_item_list(&$variables) {
             // \Drupal\Core\Render\Element::children(), which cannot be used
             // here, since it triggers an error on string values.
             foreach ($child as $child_key => $child_value) {
-              if ($child_key[0] !== '#') {
+              if (is_int($child_key) || $child_key === '' || $child_key[0] !== '#') {
                 $child['#items'][$child_key] = $child_value;
                 unset($child[$child_key]);
               }
diff --git a/core/lib/Drupal/Core/Routing/CompiledRoute.php b/core/lib/Drupal/Core/Routing/CompiledRoute.php
index 652acc5bb4..58498ce455 100644
--- a/core/lib/Drupal/Core/Routing/CompiledRoute.php
+++ b/core/lib/Drupal/Core/Routing/CompiledRoute.php
@@ -143,23 +143,22 @@ public function getRequirements() {
   /**
    * {@inheritdoc}
    */
-  public function serialize() {
+  public function __serialize(): array {
     // Calling the parent method is safer than trying to optimize out the extra
     // function calls.
-    $data = unserialize(parent::serialize());
+    $data = parent::__serialize();
     $data['fit'] = $this->fit;
     $data['patternOutline'] = $this->patternOutline;
     $data['numParts'] = $this->numParts;
 
-    return serialize($data);
+    return $data;
   }
 
   /**
    * {@inheritdoc}
    */
-  public function unserialize($serialized) {
-    parent::unserialize($serialized);
-    $data = unserialize($serialized);
+  public function __unserialize(array $data): void {
+    parent::__unserialize($data);
 
     $this->fit = $data['fit'];
     $this->patternOutline = $data['patternOutline'];
diff --git a/core/modules/taxonomy/src/Plugin/migrate/source/d6/TermLocalizedTranslation.php b/core/modules/taxonomy/src/Plugin/migrate/source/d6/TermLocalizedTranslation.php
index 844fb858b5..d8308c72b4 100644
--- a/core/modules/taxonomy/src/Plugin/migrate/source/d6/TermLocalizedTranslation.php
+++ b/core/modules/taxonomy/src/Plugin/migrate/source/d6/TermLocalizedTranslation.php
@@ -70,7 +70,13 @@ public function prepareRow(Row $row) {
     $query->condition('lt.language', $language);
     $query->addField('lt', 'translation');
     $results = $query->execute()->fetchAssoc();
-    $row->setSourceProperty($other_property . '_translated', $results['translation']);
+    if ($results) {
+      $row->setSourceProperty($other_property . '_translated', $results['translation']);
+    }
+    else {
+      // The translation does not exist.
+      $row->setSourceProperty($other_property . '_translated', NULL);
+    }
 
     parent::prepareRow($row);
   }
diff --git a/core/modules/views/tests/src/Kernel/Plugin/FieldOrLanguageJoinTest.php b/core/modules/views/tests/src/Kernel/Plugin/FieldOrLanguageJoinTest.php
index 34e4f93000..76be7154df 100644
--- a/core/modules/views/tests/src/Kernel/Plugin/FieldOrLanguageJoinTest.php
+++ b/core/modules/views/tests/src/Kernel/Plugin/FieldOrLanguageJoinTest.php
@@ -137,7 +137,7 @@ public function testLanguageBundleConditions() {
     // condition.
     $configuration = [
       'table' => 'node__field_tags',
-      'left_table' => 'node',
+      'left_table' => 'views_test_data',
       'left_field' => 'nid',
       'field' => 'entity_id',
       'extra' => [
@@ -148,7 +148,7 @@ public function testLanguageBundleConditions() {
       ],
     ];
     $join_info = $this->buildJoin($view, $configuration, 'node__field_tags');
-    $this->assertContains('AND (node__field_tags.langcode = .langcode)', $join_info['condition']);
+    $this->assertContains('AND (node__field_tags.langcode = views_test_data.langcode)', $join_info['condition']);
 
     array_unshift($configuration['extra'], [
       'field' => 'deleted',
@@ -156,7 +156,7 @@ public function testLanguageBundleConditions() {
       'numeric' => TRUE,
     ]);
     $join_info = $this->buildJoin($view, $configuration, 'node__field_tags');
-    $this->assertContains('AND (node__field_tags.langcode = .langcode)', $join_info['condition']);
+    $this->assertContains('AND (node__field_tags.langcode = views_test_data.langcode)', $join_info['condition']);
 
     // Replace the language condition with a bundle condition.
     $configuration['extra'][1] = [
@@ -173,7 +173,7 @@ public function testLanguageBundleConditions() {
       'field' => 'langcode',
     ];
     $join_info = $this->buildJoin($view, $configuration, 'node__field_tags');
-    $this->assertContains('AND (node__field_tags.bundle = :views_join_condition_1 OR node__field_tags.langcode = .langcode)', $join_info['condition']);
+    $this->assertContains('AND (node__field_tags.bundle = :views_join_condition_1 OR node__field_tags.langcode = views_test_data.langcode)', $join_info['condition']);
   }
 
   /**