Adhereing to PR cakephp#5230

Harden interface for Config engine classes.

Author: hmic

en/development/configuration.rst

@@ -648,7 +648,7 @@ reader for you application::
  App::uses('Xml', 'Utility');
  class MyXmlReader implements ConfigReaderInterface {
  public function __construct($path = null) {
- if (!$path) {
+ if ($path === null) {
  $path = APP . 'Config' . DS;
  }
  $this->_path = $path;
@@ -660,7 +660,7 @@ reader for you application::
  }
 
  // As of 2.3 a dump() method is also required
- public function dump($key, $data) {
+ public function dump($key, array $data) {
  // code to dump data to file
  }
  }