Issue #2326397 by davidhernandez: Fixed Add filtering to AttributeArray.

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));
   }
 

core/tests/Drupal/Tests/Core/Template/AttributeTest.php

@@ -178,6 +178,8 @@ public function providerTestAttributeClassHelpers() {
         'himalchuli annapurna-ii',
         array('class' => array('himalchuli', 'nuptse')),
       ),
+      // Test for the removal of an empty class name.
+      array("{{ attributes.addClass('rakaposhi', '').class }}", 'rakaposhi'),
     );
   }