Freemarker not entering if/else if values are null - freemarker

Question

<#if myVar = "test">
A
<#else>
B
<#/if>
If myVar is null / not defined, neither A nor B will be output. This is fixed by adding ! after the variable:
<#if myVar! = "test">
A
<#else>
B
<#/if>
Is this intended? Because if so, it is extremely confusing and I can't imagine any user would expect it to behave this way. It is suggesting that null = "test" is somehow neither true nor false. It seems clear that null = "test" should always be considered false -- what am I missing?
Note: we have configured Freemarker to replace unknown variables with an empty string:
config.setTemplateExceptionHandler((ex, environment, out) ->
{
if (ex instanceof InvalidReferenceException)
{
try
{
out.write("");
}
catch (IOException e)
{
throw new TemplateException("Error while handling template exception.", e, environment);
}
}
else
{
throw ex;
}
});
So this would (at least I thought it would) end up being:
<#if "" = "test">
A
<#else>
B
<#/if>
In which case, I'd expect the else to be entered for sure -- but it is not.
Given this example:
<#assign myVar = null/>
<#if myVar == "test">
A
<#else>
B
</#if>
This throws the following error:
The following has evaluated to null or missing:
==> null
myVar has been evaluated to null or missing -- this seems like the source of my confusion; Freemarker does not differentiate between missing and existing-but-null values, I guess?

Answer 1

It's irrelevant if it's #if/#else or any other directive call, because when an error occurs (any kind of TemplateException, not just "missing value"), the whole statement is skipped. Not the variable resolution, not even the whole expression, but the whole statement. That's what the Manual and the Javadoc says too, like see: https://freemarker.apache.org/docs/pgui_config_errorhandling.html. Therefore, templateExceptionHandler setting is not for providing defaults for missing values. It's for handling situations that are genuinely errors. Like, someone did a mistake, something is not operational.
As of why not take the #else still. When an error occurs while evaluating the condition, the template engine just can't tell which branch would have been taken if the developers (or whoever) did not make a mistake. Picking either branch of the if/else is a gamble. (It's not even a 50-50 gamble, as the positive branch tends to be the right one considering the real world meaning of the output, yet, if anything, people expect the template engine to bet on the else branch.) So, hoping that you will print some error indicator at least, it rather doesn't pick either branch. But it's really automatic, as the whole #if/#elseif/#else thing is one big statement.

Answer 2

<#assign myVar = "test"/>
<#if myVar?? && myVar == "test">
A
<#else>
B
</#if>

Answer 3

Yes it is intended. When a variable is not defined or null, freemarker will raise an error.
It is explained in the FAQ: Why is FreeMarker so picky about null-s and missing variables, and what to do with it?
This is a design choice from the initial author of the framework. If you are not confortable with this choice, you can use the Default value operator (use myVar! instead of myVar), or use another templating framework.
The custom exception handler you added doesn't replace the expression with an empty String, it replaces the full if/else expression.