title: Upload files with Zk framework
body: <p>I need upload csv files in ZK
      this is my zul page:</p>
  
  <pre><code>&lt;zk&gt;
  &lt;window
      apply="org.zkoss.bind.BindComposer"
      viewModel="@id('vm') @init('UploadVM')"
      title="win"
      position="center"
      mode="overlapped"
      border="normal"
      width="300px"
      height="200px"&gt;
      &lt;button
          label="upload"
          upload="true,maxsize=801192"
          onUpload="@command('uploadFile',upload=event)"
          autodisable="self" /&gt;
  
  &lt;/window&gt;
  &lt;/zk&gt;
  </code></pre>
  
  <p>And my java page: </p>
  
  <pre><code>public class UploadVM {
      private Media media;
      public Media getMedia(){
          return media;
      }
      @NotifyChange("media")
      @Command
      public void uploadFile(@ContextParam(ContextType.TRIGGER_EVENT) UploadEvent event) {
          media = event.getMedia();
          media.getStreamData();
      }
  </code></pre>
  
  <p>But with this simple example i have the following error:</p>
  
  <pre><code>Use getStringData() instead
  </code></pre>
  
  <p>And i don not know what happen.</p>
  
  <p>Who can help me???</p>