Fixes #6589: updated code style guide to mention else after return, adjusted code involved in the issue

docs/internals/core-code-style.md

@@ -262,6 +262,29 @@ if (!$model && null === $event)
     throw new Exception('test');
 ```
 
+Prefer avoiding `else` after `return` where it makes sense.
+Use [guard conditions](http://refactoring.com/catalog/replaceNestedConditionalWithGuardClauses.html).
+
+```php
+$result = $this->getResult();
+if (empty($result)) {
+  return true;
+} else {
+  // process result
+}
+```
+
+is better as
+
+```php
+$result = $this->getResult();
+if (empty($result)) {
+  return true;
+}
+
+// process result
+```
+
 #### switch
 
 Use the following formatting for switch:

framework/validators/Validator.php

@@ -267,14 +267,14 @@ class Validator extends Component
         $result = $this->validateValue($value);
         if (empty($result)) {
             return true;
-        } else {
-            list($message, $params) = $result;
-            $params['attribute'] = Yii::t('yii', 'the input value');
-            $params['value'] = is_array($value) ? 'array()' : $value;
-            $error = Yii::$app->getI18n()->format($message, $params, Yii::$app->language);
-
-            return false;
         }
+
+        list($message, $params) = $result;
+        $params['attribute'] = Yii::t('yii', 'the input value');
+        $params['value'] = is_array($value) ? 'array()' : $value;
+        $error = Yii::$app->getI18n()->format($message, $params, Yii::$app->language);
+
+        return false;
     }
 
     /**