title: Uploading file in postman extension
body: <p>I try to upload an image via the postman extension, but I get the following response. Furthermore, the image does not appear in the specified directory.</p>
  
  <pre><code>{
      "name": "PHP Notice",
      "message": "Undefined index: user_id",
      "code": 8,
      "type": "yii\\base\\ErrorException",
      "file": "C:\\xampp\\htdocs\\basic14-4-2016\\controllers\\ApiuploadsController.php",
      "line": 85,
      "stack-trace": [
          "#0 C:\\xampp\\htdocs\\basic14-4-2016\\controllers\\ApiuploadsController.php(85): yii\\base\\ErrorHandler-&gt;handleError(8, 'Undefined index...', 'C:\\\\xampp\\\\htdocs...', 85, Array)",
          "#1 [internal function]: app\\controllers\\ApiuploadsController-&gt;actionNew()",
          "#2 C:\\xampp\\htdocs\\basic14-4-2016\\vendor\\yiisoft\\yii2\\base\\InlineAction.php(55): call_user_func_array(Array, Array)",
          "#3 C:\\xampp\\htdocs\\basic14-4-2016\\vendor\\yiisoft\\yii2\\base\\Controller.php(151): yii\\base\\InlineAction-&gt;runWithParams(Array)",
          "#4 C:\\xampp\\htdocs\\basic14-4-2016\\vendor\\yiisoft\\yii2\\base\\Module.php(455): yii\\base\\Controller-&gt;runAction('new', Array)",
          "#5 C:\\xampp\\htdocs\\basic14-4-2016\\vendor\\yiisoft\\yii2\\web\\Application.php(84): yii\\base\\Module-&gt;runAction('apiuploads/new', Array)",
          "#6 C:\\xampp\\htdocs\\basic14-4-2016\\vendor\\yiisoft\\yii2\\base\\Application.php(375): yii\\web\\Application-&gt;handleRequest(Object(yii\\web\\Request))",
          "#7 C:\\xampp\\htdocs\\basic14-4-2016\\web\\index.php(12): yii\\base\\Application-&gt;run()",
          "#8 {main}"
      ]
  }
  </code></pre>