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

vendor/symfony/validator/Constraint.php

@@ -129,6 +129,9 @@ abstract class Constraint
             unset($options['value']);
         }
 
+        if (is_array($options)) {
+            reset($options);
+        }
         if (is_array($options) && count($options) > 0 && is_string(key($options))) {
             foreach ($options as $option => $value) {
                 if (array_key_exists($option, $knownOptions)) {
@@ -207,8 +210,6 @@ abstract class Constraint
      * @throws InvalidOptionsException If an invalid option name is given
      *
      * @internal This method should not be used or overwritten in userland code.
-     *
-     * @since 2.6
      */
     public function __get($option)
     {
@@ -296,8 +297,6 @@ abstract class Constraint
      * @internal This method may be replaced by an implementation of
      *           {@link \Serializable} in the future. Please don't use or
      *           overwrite it.
-     *
-     * @since 2.6
      */
     public function __sleep()
     {