title: express-validator/node-validator: how to validate that property exists, and should be present
body: <p>is there a validation like:</p>
  
  <pre><code>req.checkBody('property', 'should be present').isPresent();
  </code></pre>
  
  <p>The value itself, does not matter.</p>
  
  <p>for now i use this solution:<br>
  <code>.isLength()</code></p>
  
  <p><strong>update</strong><br>
  - <code>.isLength()</code> is a bad solution, because it tests if the value is a string.<br>
  - and you can not send POST value as 'undefined' from your browser, because of JSON.stringify method, that ignores such properties.
  So the validation against <code>!== undefined</code> should be enough.</p>