default values for db\Connection username and password to null

fixes #1821

framework/CHANGELOG.md

@@ -68,6 +68,7 @@ Yii Framework 2 Change Log
 - Chg #1647: Changed the default CSS class of error block to be `error-block` (qiangxue)
 - Chg #1796: Removed `yii\base\Controller::getActionParams()` (samdark)
 - Chg #1835: `CheckboxColumn` now renders checkboxes whose values are the corresponding data key values (qiangxue)
+- Chg #1821: Changed default values for yii\db\Connection username and password to null (cebe)
 - Chg: Renamed `yii\jui\Widget::clientEventsMap` to `clientEventMap` (qiangxue)
 - Chg: Renamed `ActiveRecord::getPopulatedRelations()` to `getRelatedRecords()` (qiangxue)
 - Chg: Renamed `attributeName` and `className` to `targetAttribute` and `targetClass` for `UniqueValidator` and `ExistValidator` (qiangxue)

framework/yii/db/Connection.php

@@ -118,13 +118,13 @@ class Connection extends Component
 	 */
 	public $dsn;
 	/**
-	 * @var string the username for establishing DB connection. Defaults to empty string.
+	 * @var string the username for establishing DB connection. Defaults to `null` meaning no username to use.
 	 */
-	public $username = '';
+	public $username;
 	/**
-	 * @var string the password for establishing DB connection. Defaults to empty string.
+	 * @var string the password for establishing DB connection. Defaults to `null` meaning no password to use.
 	 */
-	public $password = '';
+	public $password;
 	/**
 	 * @var array PDO attributes (name => value) that should be set when calling [[open()]]
 	 * to establish a DB connection. Please refer to the