Update to Drupal 8.2.0. For more information, see https://www.drupal.org/project/drupal/releases/8.2.0

core/lib/Drupal/Core/StringTranslation/Translator/TranslatorInterface.php

@@ -17,7 +17,7 @@ interface TranslatorInterface {
    * @param string $context
    *   The string context.
    *
-   * @return string|FALSE
+   * @return string|false
    *   Translated string if there is a translation, FALSE if not.
    */
   public function getStringTranslation($langcode, $string, $context);