[Templating] UndefinedLiteral Coerced To Null

[chadhietala]

Currently in both rendering engines UndefinedLiterals are coerced to null. This seems incorrect, however there may be application code that is dependent on this incorrectness, which may lead to non-obvious breakages.

Example:

{{foo-helper undefined}}

function fooHelper(params, hash) {
  assert(params[0] === null);
}

This issue is a placeholder to see if anybody is surprised by this or has code that coerces null back into undefined.

[mitchlloyd]

I was surprised by this recently when writing a helper test to handle undefined values. I had to use {{my-helper nothing}} instead of {{my-helper undefined}}. Now I know why :)

My vote would be to change the behavior to pass the expected undefined value. Although it could be breaking, relying on {{foo-helper undefined}} being coerced to null would most likely be an accident.

[chadhietala]

@mitchlloyd This is my predicament as well.

[pixelhandler]

@chadhietala does glimmerjs/glimmer-vm#252 resolve this issue?

[chadhietala]

No waiting on glimmerjs/glimmer-vm#255

[chadhietala]

glimmerjs/glimmer-vm#255 has landed but I want to keep this open until we bump the version on glimmer.

[rwjblue]

Closed by #14060