diff --git a/core/lib/Drupal/Core/Template/AttributeArray.php b/core/lib/Drupal/Core/Template/AttributeArray.php
index c432ba0..dbe8089 100644
--- a/core/lib/Drupal/Core/Template/AttributeArray.php
+++ b/core/lib/Drupal/Core/Template/AttributeArray.php
@@ -66,6 +66,8 @@ public function offsetExists($offset) {
    * Implements the magic __toString() method.
    */
   public function __toString() {
+    // Filter out any empty values before printing.
+    $this->value = array_filter($this->value);
     return String::checkPlain(implode(' ', $this->value));
   }