How to set null to a variable in freemarker

Question

I can't find anything related to this on any question, and it is something really basic, but I can't figure it out.

So my problem is that I don't know how to set null to a variable in freemarker. Example:

${hi!"bye"}          <#-- Prints "bye" because hi is undefined -->
<#assign hi="hi">    <#-- Sets a value to the var hi -->
${hi!"bye"}          <#-- Prints "hi" because hi has a value -->
<#assign hi=null>    <#-- This does not work but is what I am looking for -->
${hi!"bye"}          <#-- I want it to print "bye" because hi should be undefined -->

I have this problem because I iterate over a list and set a var if some logic to the specific item validates, and then check if the var exists, but if the first item creates the var, then I will have the var set for the rest of the items in the list.

Answer 1

No, there's no "unassign", nor the concept of null exists in FreeMarker (until 2.4.0 at least, but that's far away anyway). It only have missing variables (maybe technically a null, maybe doesn't exist at all) and those that are there. I don't really get why is that needed in your case. Can you show a simplified example of the situation?