How to check if a variable exists in a FreeMarker template?

Question

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

Answer 1

To check if the value exists:

[#if userName??]
   Hi ${userName}, How are you?
[/#if]

Or with the standard freemarker syntax:

<#if userName??>
   Hi ${userName}, How are you?

To check if the value exists and is not empty:

<#if userName?has_content>
    Hi ${userName}, How are you?