title: Yii2: $model->load() returns false
body: <p>I have a form where user can load the image. In my controller I have an action called <em>actionUpdate</em> which contains code like this.<br>
  <strong>Controller</strong></p>
  
  <pre><code>public function actionUpdate()
  {
      $id = Yii::$app-&gt;user-&gt;id;
      $model = Page::find()-&gt;where(['user_id'=&gt;$id])-&gt;one();
      if ($model-&gt;load(Yii::$app-&gt;request-&gt;post()))
      {
          $image = UploadedFile::getInstance($model, 'thumbnail');
          $model-&gt;thumbnail = $model-&gt;url.".".$image-&gt;extension;
  
          if ($model-&gt;validate() &amp;&amp; $model-&gt;save())
          {
              $model-&gt;upload();
              //page/url is for the user's page
              return $this-&gt;redirect('page/'.$model-&gt;url);
          } 
      } 
      else 
      {
          //'update' is a view file with form
          return $this-&gt;render('update', [
              'model' =&gt; $model,
          ]);
      }
  }
  </code></pre>
  
  <p>When I'm submitting the form, I'm being redirected to the same update action url but with blank screen, instead of redirecting to the user's page. Maybe the problem is in my Model's upload function?
  <br>
  <strong>Model</strong></p>
  
  <pre><code>public function upload()
  {
      if ($this-&gt;validate()) {
          $user = Page::find()-&gt;where(["user_id" =&gt; Yii::$app-&gt;user-&gt;id])-&gt;one();
          $this-&gt;thumbnail-&gt;saveAs('avatars/'.$user-&gt;url.'.'.$this-&gt;thumbnail-&gt;extension);
          return true;
      } else {
          return false;
      }
  }
  </code></pre>