haxe.Template: "Uncaught Error: Unexpected 'false'"

When I try to do something with a return value of a so-called "macro" of `haxe.Template`, I get an error:

> "Uncaught Error: Unexpected 'false'"
```haxe
// test 1. Getting actual value just works
var input = "$$getSetting(\"MY_ID\") WORKS..";
var template = new haxe.Template(input);
trace(template.execute({}, {
getSetting: function(_, id:String) return id.toUpperCase(),
}));

// test 2. Doing something with return value doesn't work
var input = "
::if ($$getSetting(\"MY_ID\").length > 0)::
YESSS
::else::
NOOOO
::end::
";
var template = new haxe.Template(input);
trace(template.execute({}, {
getSetting: function(_, id:String) return id.toUpperCase(),
}));
```
https://try.haxe.org/#ce079

Seen on Haxe 3.4.2, Haxe/JavaScript target