Freemarker shortcut for boolean: "is not null and is true"

Question

This seems to show "Hello world" if foobar is defined

<#if foobar??>
    Hello world
</#if>

If foobar is a boolean, what do I use to write Hello world if foobar is both defined AND true?

Answer 1

The shortest I can think of is specifying a false default value:

<#if foobar!false>
    Hello world
</#if>