Update to Drupal 8.1.0. For more information, see https://www.drupal.org/drupal-8.1.0-release-notes

vendor/symfony/validator/Constraints/Regex.php

@@ -21,6 +21,12 @@ use Symfony\Component\Validator\Constraint;
  */
 class Regex extends Constraint
 {
+    const REGEX_FAILED_ERROR = 'de1e3db3-5ed4-4941-aae4-59f3667cc3a3';
+
+    protected static $errorNames = array(
+        self::REGEX_FAILED_ERROR => 'REGEX_FAILED_ERROR',
+    );
+
     public $message = 'This value is not valid.';
     public $pattern;
     public $htmlPattern;