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

vendor/symfony/polyfill-php54/Php54.php

@@ -31,12 +31,6 @@ final class Php54
             return false;
         }
 
-        $data = pack('H*', $data);
-
-        if (false !== strpos($data, "\0")) {
-            return false;
-        }
-
-        return $data;
+        return pack('H*', $data);
     }
 }