Check for UPLOAD_ERR_NO_FILE in UploadedFile

framework/CHANGELOG.md

@@ -66,6 +66,7 @@ Yii Framework 2 Change Log
 - Bug #4127: `CaptchaValidator` clientside error message wasn't formed properly (samdark)
 - Bug #4162: Fixed bug where schema name was not used in ’SHOW CREATE TABLE’ query in `yii\db\mysql\Schema` (stevekr)
 - Bug #4241: `yii\widgets\Pjax` was incorrectly setting container id (mitalcoi)
+- Bug #4276: Added check for UPLOAD_ERR_NO_FILE in `yii\web\UploadedFile` and return null if no file was uploaded (OmgDef)
 - Bug: Fixed inconsistent return of `\yii\console\Application::runAction()` (samdark)
 - Bug: URL encoding for the route parameter added to `\yii\web\UrlManager` (klimov-paul)
 - Bug: Fixed the bug that requesting protected or private action methods would cause 500 error instead of 404 (qiangxue)

framework/web/UploadedFile.php

@@ -223,7 +223,7 @@ class UploadedFile extends Object
             foreach ($names as $i => $name) {
                 self::loadFilesRecursive($key . '[' . $i . ']', $name, $tempNames[$i], $types[$i], $sizes[$i], $errors[$i]);
             }
-        } else {
+        } elseif ($errors !== UPLOAD_ERR_NO_FILE) {
             self::$_files[$key] = new static([
                 'name' => $names,
                 'tempName' => $tempNames,