Fixes #4736

framework/behaviors/BlameableBehavior.php

@@ -102,13 +102,9 @@ class BlameableBehavior extends AttributeBehavior
     protected function getValue($event)
     {
         if ($this->value === null) {
-            if (Yii::$app->hasMethod('getUser')) {
-                $user = Yii::$app->getUser();
+            $user = Yii::$app->get('user', false);
             return $user && !$user->isGuest ? $user->id : null;
         } else {
-                return null;
-            }
-        } else {
             return call_user_func($this->value, $event);
         }
     }