title: How to check if a variable exists in a FreeMarker template?
body: <p>I have a Freemarker template which contains a bunch of placeholders for which values are supplied when the template is processed. I want to conditionally include part of the template if the userName variable is supplied, something like:</p>
  
  <pre><code>[#if_exists userName]
    Hi ${userName}, How are you?
  [/#if_exists]
  </code></pre>
  
  <p>However, the FreeMarker manual seems to indicate that if_exists is deprecated, but I can't find another way to achieve this. Of course, I could simple providing an additional boolean variable isUserName and use that like this:</p>
  
  <pre><code>[#if isUserName]
    Hi ${userName}, How are you?
  [/#if]
  </code></pre>
  
  <p>But if there's a way of checking whether userName exists then I can avoid adding this extra variable.</p>