Add failing test for autocomplete with dynamic type

[lencioni]

This will cause axe to throw an error like:

TypeError: Cannot read property 'replace' of null

I believe that the problem might be related to getLiteralPropValue
returning null instead of undefined for dynamic props.

[ljharb]

I pushed up a fix, but this is really a workaround for what's likely a bug in axe caused by using default values and forgetting that that doesn't handle null. Would you mind filing an issue upstream for it?

[lencioni]

Happy to file a bug upstream, but I'm not sure I understand what you mean by this:

caused by using default values and forgetting that that doesn't handle null

[ljharb]

hmm, the stack trace points to https://github.com/dequelabs/axe-core/blob/8a4d9b0970ad909100856faf102f14fea4d6c268/lib/commons/text/sanitize.js - but that would fail on undefined too, so my assumption (which may be incorrect) is that they've got code like function foo(x = '') { return x.replace(…); }, which would work for undefined or a string but not for null.

It's really hard to figure out where the error is, though, since they apparently bundle the library :-/

[jessebeach]

Thanks @lencioni !

Let's get this patch in. @WilcoFiers, the underlying issue here is with aXe; @ljharb has some theories in the comments above.