core/lib/Drupal/Core/Menu/MenuLinkTree.php          |  3 ++-
 core/lib/Drupal/Core/Render/Element.php             | 16 ++++++++++++++++
 core/modules/block/src/BlockViewBuilder.php         |  2 +-
 core/tests/Drupal/Tests/Core/Render/ElementTest.php | 21 +++++++++++++++++++++
 4 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/core/lib/Drupal/Core/Menu/MenuLinkTree.php b/core/lib/Drupal/Core/Menu/MenuLinkTree.php
index 9d95501..332a2c7 100644
--- a/core/lib/Drupal/Core/Menu/MenuLinkTree.php
+++ b/core/lib/Drupal/Core/Menu/MenuLinkTree.php
@@ -8,6 +8,7 @@
 namespace Drupal\Core\Menu;
 
 use Drupal\Component\Utility\NestedArray;
+use Drupal\Core\Access\AccessResultInterface;
 use Drupal\Core\Cache\CacheableMetadata;
 use Drupal\Core\Cache\CacheBackendInterface;
 use Drupal\Core\Controller\ControllerResolverInterface;
@@ -179,7 +180,7 @@ public function build(array $tree, $level = 0) {
       $tree_link_cacheability = $tree_link_cacheability->merge(CacheableMetadata::createFromObject($data->link));
 
       // Only render accessible links.
-      if (!$data->access->isAllowed()) {
+      if ($data->access instanceof AccessResultInterface && !$data->access->isAllowed()) {
         continue;
       }
 
diff --git a/core/lib/Drupal/Core/Render/Element.php b/core/lib/Drupal/Core/Render/Element.php
index 094a7d5..256b5e3 100644
--- a/core/lib/Drupal/Core/Render/Element.php
+++ b/core/lib/Drupal/Core/Render/Element.php
@@ -177,4 +177,20 @@ public static function setAttributes(array &$element, array $map) {
     }
   }
 
+  /**
+   * Indicates whether the given element is empty.
+   *
+   * An element that only has #cache set is considered empty, because it will
+   * render to the empty string.
+   *
+   * @param array $elements
+   *   The element.
+   *
+   * @return bool
+   *   Whether the given element is empty.
+   */
+  public static function isEmpty(array $elements) {
+    return empty($elements) || count($elements) === 1 && array_keys($elements) === ['#cache'];
+  }
+
 }
diff --git a/core/modules/block/src/BlockViewBuilder.php b/core/modules/block/src/BlockViewBuilder.php
index 5b94d5c..f674d68 100644
--- a/core/modules/block/src/BlockViewBuilder.php
+++ b/core/modules/block/src/BlockViewBuilder.php
@@ -105,7 +105,7 @@ public function buildBlock($build) {
     // Remove the block entity from the render array, to ensure that blocks
     // can be rendered without the block config entity.
     unset($build['#block']);
-    if (!empty($content) && !(count($content) === 1 && array_keys($content) === ['#cache'])) {
+    if (!Element::isEmpty($content)) {
       // Place the $content returned by the block plugin into a 'content' child
       // element, as a way to allow the plugin to have complete control of its
       // properties and rendering (e.g., its own #theme) without conflicting
diff --git a/core/tests/Drupal/Tests/Core/Render/ElementTest.php b/core/tests/Drupal/Tests/Core/Render/ElementTest.php
index 0d764cd..8220d99 100644
--- a/core/tests/Drupal/Tests/Core/Render/ElementTest.php
+++ b/core/tests/Drupal/Tests/Core/Render/ElementTest.php
@@ -179,4 +179,25 @@ public function providerTestSetAttributes() {
     );
   }
 
+  /**
+   * @covers ::isEmpty
+   *
+   * @dataProvider providerTestIsEmpty
+   */
+  public function testIsEmpty(array $element, $expected) {
+    $this->assertSame(Element::isEmpty($element), $expected);
+  }
+
+  public function providerTestIsEmpty() {
+    return [
+      [[], TRUE],
+      [['#cache' => []], TRUE],
+      [['#cache' => ['tags' => ['foo']]], TRUE],
+      [['#cache' => ['contexts' => ['bar']]], TRUE],
+
+      [['#cache' => [], '#any_other_property' => TRUE], FALSE],
+      [['#any_other_property' => TRUE], FALSE],
+    ];
+  }
+
 }