Fixed typo

Author: samdark

docs/guide/input-validation.md

@@ -214,7 +214,7 @@ if they are empty. You can do so by using the [default](tutorial-core-validators
 ```
 
 By default, an input is considered empty if its value is an empty string, an empty array or a null.
-You may customize the default empty detection logic by configuring the the [[yii\validators\Validator::isEmpty]] property
+You may customize the default empty detection logic by configuring the [[yii\validators\Validator::isEmpty]] property
 with a PHP callable. For example,
 
 ```php