Update to Drupal 8.2.6. For more information, see https://www.drupal.org/project/drupal/releases/8.2.6

vendor/symfony/console/Helper/HelperSet.php

@@ -21,13 +21,16 @@ use Symfony\Component\Console\Exception\InvalidArgumentException;
  */
 class HelperSet implements \IteratorAggregate
 {
+    /**
+     * @var Helper[]
+     */
     private $helpers = array();
     private $command;
 
     /**
      * Constructor.
      *
-     * @param Helper[] $helpers An array of helper.
+     * @param Helper[] $helpers An array of helper
      */
     public function __construct(array $helpers = array())
     {
@@ -110,6 +113,9 @@ class HelperSet implements \IteratorAggregate
         return $this->command;
     }
 
+    /**
+     * @return Helper[]
+     */
     public function getIterator()
     {
         return new \ArrayIterator($this->helpers);