Update to Drupal 8.1.2. For more information, see https://www.drupal.org/project/drupal/releases/8.1.2

core/modules/book/src/BookOutlineStorageInterface.php

@@ -49,7 +49,6 @@ interface BookOutlineStorageInterface {
    *
    * @param array $book_link
    *   The book link.
-   *
    * @param int $max_depth
    *   The maximum supported depth of the book tree.
    *
@@ -166,4 +165,5 @@ interface BookOutlineStorageInterface {
    *   Array of unordered subtree book items.
    */
   public function getBookSubtree($link, $max_depth);
+
 }