title: Vue return undefined during emit event
body: <p>I read a code, where it allows user to download attachment</p>
  <pre class="lang-html prettyprint-override"><code>  &lt;template #link=&quot;{ item, rowdata }&quot;&gt;
      &lt;attachment-link
        v-test-id=&quot;'attachment-link'&quot;
        :inventory-id=&quot;item&quot;
        :filename=&quot;rowdata['fileName']&quot;
        @download-attachment=&quot;downloadAttachment&quot;&gt;
      &lt;/attachment-link&gt;
    &lt;/template&gt;
  </code></pre>
  <p>But in the <code>downloadAttachment</code> function, it returns <code>undefined</code>, why the emit still works?</p>
  <pre class="lang-js prettyprint-override"><code>@Emit('download')
  private downloadAttachment(filename: string, attachmentId: string) {
    return undefined;
  }
  </code></pre>