title: Ext JS xtemplate question - check if field exists
body: <p>I have an ExtJS xtemplate that is throwing errors because of the way a json object is returned.</p>
  
  <p>Sometimes the json object has a field <code>customer</code> defined, but sometimes it's completely missing from the object.</p>
  
  <p>Obviously, I get an error <strong>customer is not defined</strong> when applying my template to the json where the field is missing.</p>
  
  <p>So my question is:<br>
  Is there a way that I can check for an undefined field in an xtemplate?</p>
  
  <p>Like:</p>
  
  <pre><code>&lt;tpl if="customer!=undefined"&gt;{customer}&lt;/tpl&gt;
  </code></pre>
  
  <p>obviously I've tried this but it doesn't work.</p>
  
  <p>Thanks for any help.</p>