diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index 7722301..1ed2caa 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -2098,12 +2098,7 @@ function theme_table($variables) {
     drupal_add_library('system', 'drupal.tableheader');
     // Add 'sticky-enabled' class to the table to identify it for JS.
     // This is needed to target tables constructed by this function.
-    if (isset($attributes['class'])) {
-      $attributes['class'][] = 'sticky-enabled';
-    }
-    else {
-      $attributes['class'] = array('sticky-enabled');
-    }
+    $attributes['class'][] = 'sticky-enabled';
   }
   // If the table has headers and it should react responsively to columns hidden
   // with the classes represented by the constants RESPONSIVE_PRIORITY_MEDIUM
@@ -2112,12 +2107,7 @@ function theme_table($variables) {
     drupal_add_library('system', 'drupal.tableresponsive');
     // Add 'responsive-enabled' class to the table to identify it for JS.
     // This is needed to target tables constructed by this function.
-    if (isset($attributes['class'])) {
-      $attributes['class'][] = 'responsive-enabled';
-    }
-    else {
-      $attributes['class'] = array('responsive-enabled');
-    }
+    $attributes['class'][] = 'responsive-enabled';
   }
 
   $output = '<table' . new Attribute($attributes) . ">\n";
diff --git a/core/modules/block/lib/Drupal/block/Tests/BlockStorageUnitTest.php b/core/modules/block/lib/Drupal/block/Tests/BlockStorageUnitTest.php
index 07e56d1..7b826ad 100644
--- a/core/modules/block/lib/Drupal/block/Tests/BlockStorageUnitTest.php
+++ b/core/modules/block/lib/Drupal/block/Tests/BlockStorageUnitTest.php
@@ -143,7 +143,7 @@ protected function renderTests() {
     $expected[] = '  ';
     $expected[] = '    ';
     $expected[] = '';
-    $expected[] = '  <div class="content">';
+    $expected[] = '  <div class="content ">';
     $expected[] = '   ';
     $expected[] = '  </div>';
     $expected[] = '</div>';
@@ -163,7 +163,7 @@ protected function renderTests() {
     $expected[] = '      <h2 class="">Powered by Bananas</h2>';
     $expected[] = '    ';
     $expected[] = '';
-    $expected[] = '  <div class="content">';
+    $expected[] = '  <div class="content ">';
     $expected[] = '   ';
     $expected[] = '  </div>';
     $expected[] = '</div>';
diff --git a/core/modules/block/templates/block.html.twig b/core/modules/block/templates/block.html.twig
index b7b2342..3ee0154 100644
--- a/core/modules/block/templates/block.html.twig
+++ b/core/modules/block/templates/block.html.twig
@@ -37,14 +37,14 @@
  @todo Remove the div around content - and make sure this doesn't break any
   CSS defined in modules.
 #}
-<div id="{{ attributes.id }}" class="block {{- attributes.class }}"{{ attributes }}>
+<div id="{{ attributes.id }}" class="block {{ attributes.class }}"{{ attributes }}>
   {{ title_prefix }}
   {% if label %}
     <h2{{ title_attributes }}>{{ label }}</h2>
   {% endif %}
   {{ title_suffix }}
 
-  <div class="content {{- content_attributes.class }}"{{ content_attributes }}>
+  <div class="content {{ content_attributes.class }}"{{ content_attributes }}>
    {{ content }}
   </div>
 </div>