diff --git a/core/modules/block/block.module b/core/modules/block/block.module
index 42f22fa..d9d2106 100644
--- a/core/modules/block/block.module
+++ b/core/modules/block/block.module
@@ -350,7 +350,7 @@ function _block_get_renderable_region($list = array()) {
     // skip the help block, since we assume that most users do not need or want
     // to perform contextual actions on the help block, and the links needlessly
     // draw attention on it.
-    if (!in_array($block->get('plugin'), array('system_help_block', 'system_main_block'))) {
+    if (isset($build[$key]) && !in_array($block->get('plugin'), array('system_help_block', 'system_main_block'))) {
       $build[$key]['#contextual_links']['block'] = array('admin/structure/block/manage', array($key));
     }
   }
diff --git a/core/modules/block/lib/Drupal/block/Tests/BlockTest.php b/core/modules/block/lib/Drupal/block/Tests/BlockTest.php
index b746b21..9020087 100644
--- a/core/modules/block/lib/Drupal/block/Tests/BlockTest.php
+++ b/core/modules/block/lib/Drupal/block/Tests/BlockTest.php
@@ -59,6 +59,7 @@ function testBlockVisibility() {
 
     // Confirm that an empty block is not displayed.
     $this->assertNoText('Powered by Drupal', 'Empty block not displayed.');
+    $this->assertNoRaw('sidebar-first', 'Empty sidebar-first region is not displayed.');
   }
 
   /**