note about empty values for datepicker and validator

fixes #5580

docs/guide/tutorial-core-validators.md

@@ -97,7 +97,7 @@ is as specified by the `operator` property.
 
 ```php
 [
-    [['from', 'to'], 'date'],
+    [['from_date', 'to_date'], 'date'],
 ]
 ```
 
@@ -113,6 +113,13 @@ specified via [[yii\validators\DateValidator::timestampAttribute|timestampAttrib
 - `timestampAttribute`: the name of the attribute to which this validator may assign the UNIX timestamp
   converted from the input date/time.
 
+In case the input is optional you may also want to add a default value filter in addition to the date validator
+to ensure empty input is stored as `NULL`. Other wise you may end up with dates like `0000-00-00` in your database
+or `1970-01-01` in the input field of a date picker.
+
+```php
+[['from_date', 'to_date'], 'default', 'value' => null],
+```
 
 ## [[yii\validators\DefaultValueValidator|default]] <a name="default"></a>
 

extensions/jui/DatePicker.php

@@ -38,6 +38,14 @@ use yii\helpers\Json;
  * ]);
  * ```
  *
+ * Note that empty values like empty strings and 0 will result in a date displayed as `1970-01-01`.
+ * So to make sure empty values result in an empty text field in the datepicker you need to add a
+ * validation filter in your model that sets the value to `null` in case when no date has been entered:
+ *
+ * ```php
+ * [['from_date'], 'default', 'value' => null],
+ * ```
+ *
  * @see http://api.jqueryui.com/datepicker/
  * @author Alexander Kochetov <creocoder@gmail.com>
  * @author Carsten Brandt <mail@cebe.cc>