Did an error come up in your testing? The $userdata param should be null (default value from the method signature) if no argument is provided, which should be fine to pass into the array_walk...?

I did yes; check out the latter half of #2. It's complaining that the parameter passed to the $callable needs to be a boolean but we're passing null. Based on the array_walk docs, the $userdata parameter is optional hence the solution I used here. If there is a better way to solve I'd love to know because it doesn't seem like the cleanest method 🤔

A ha! So, you're right — we need to only pass that parameter downstream if the argument is actually provided — but it has nothing to do with array_walk.

Specifically, array_walk doesn't care what kind of argument is passed there. It's the downstream method that cares. (In this case, saveElement is looking for a boolean param, probably to toggle some validation logic. The fact that we were passing a default null was fine with array_walk, but saveElement complained.)

We can't predict whether a target method will ever expect a second param, so we shouldn't presume to put a default value there. We should let our user do that, in cases where they know it's relevant to the target method.

However, a simple truthiness check isn't a good idea here. (What if the $userdata is false, or null, or [], or 0, or anything else that casts to a false boolean? That argument will never be passed through.) The correct check to use here is isset().