Update docblock.

src/Controller/Component/CookieComponent.php

@@ -337,8 +337,8 @@ class CookieComponent extends Component {
  * Get / set encryption type. Use this method in ex: AppController::beforeFilter()
  * before you have read or written any cookies.
  *
- * @param string $type Encryption method
- * @return string
+ * @param string|null $type Encryption type to set or null to get current type.
+ * @return string|null
  * @throws \Cake\Error\Exception When an unknown type is used.
  */
 	public function encryption($type = null) {