diff --git a/core/lib/Drupal/Core/Template/Attribute.php b/core/lib/Drupal/Core/Template/Attribute.php
index 7ea9b4c..abd889a 100644
--- a/core/lib/Drupal/Core/Template/Attribute.php
+++ b/core/lib/Drupal/Core/Template/Attribute.php
@@ -143,7 +143,12 @@ public function addClass() {
         // Merge the values passed in from the classes array.
         // The argument is cast to an array to support comma separated single
         // values or one or more array arguments.
-        $classes = array_merge($classes, (array) $arg);
+        // We also filter out any empty values from the array.
+        $classes = array_filter(array_merge($classes, (array) $arg));
+      }
+      // If there are no classes to add, return early.
+      if (empty($classes)) {
+        return $this;
       }
 
       // Merge if there are values, just add them otherwise.
diff --git a/core/tests/Drupal/Tests/Core/Template/AttributeTest.php b/core/tests/Drupal/Tests/Core/Template/AttributeTest.php
index 9f2cb50..a5cad7b 100644
--- a/core/tests/Drupal/Tests/Core/Template/AttributeTest.php
+++ b/core/tests/Drupal/Tests/Core/Template/AttributeTest.php
@@ -69,6 +69,25 @@ public function testAddClasses() {
     $attribute->addClass();
     $this->assertEmpty($attribute['class']);
 
+    // Test various permutations of adding values to empty Attribute objects.
+    foreach (array(NULL, FALSE, '', []) as $value) {
+      // Single value.
+      $attribute->addClass($value);
+      $this->assertEmpty($attribute['class']);
+
+      // Multiple values.
+      $attribute->addClass($value, $value);
+      $this->assertEmpty($attribute['class']);
+
+      // Single value in array.
+      $attribute->addClass([$value]);
+      $this->assertEmpty($attribute['class']);
+
+      // Single value in arrays.
+      $attribute->addClass([$value], [$value]);
+      $this->assertEmpty($attribute['class']);
+    }
+
     // Add one class on empty attribute.
     $attribute->addClass('banana');
     $this->assertArrayEquals(array('banana'), $attribute['class']->value());