ENH PHP 8.1 compatibility

[emteknetnz]

Issue silverstripe/silverstripe-framework#10250

[GuySartorelli]

Builds are failing - can you please take a look?

[emteknetnz]

.travis.yml required a ^4 of webauthn, which is currently not php 8.1 compatible. I've changed to 4.x-dev, it'll still fail until https://github.com/silverstripe/silverstripe-webauthn-authenticator/pulls is merged

[GuySartorelli]

For posterity: See discussion in silverstripe/silverstripe-admin#1294 about the general approach. tl;dr:

the purposes of this PR is to avoid passing null (specifically null) from built-in functions that as of php 8.1 will throw deprecation warnings if null is passed in. The approach is necessarily heavy-handed, and while there are many situations where it isn't needed, it would be prohibitively laborious to find all of those situations by hand.

Looks good to me - but @emteknetnz can you please validate that the travis build not failing is okay? Based on your previous comment it sounds like it was expected to fail?

[emteknetnz]

Ah, might have been this older commit that was required - silverstripe/silverstripe-webauthn-authenticator@371c5bb

[GuySartorelli]

Sweet. I'll add this to my merge list for this afternoon.