Generated type for MultiCheckbox wrong

[kynx]

I'm getting something like:

''|'0'|'1'|'2'|null

It should be:

array<''|'0'|'1'|'2'|null>

Actually what is submitted is an array. I think this is down to the Explode validator - it can accept a comma separated list, explode it and validate the contents, but this one is configured with a null delimiter. The ExplodeVisitor would do the right thing if it knew the incoming data was already an array, but right now we have no way of telling it that.

One way to tackle that would be to convert it's Input to an ArrayInput before we process it, a bit like we do for single-element collections. But the logic there is already getting pretty soupy - we probably need it separate it out into some kind of ElementVisitorInterface.