The fix for the issue is relatively easy and there are multiple options available, though some could result in BC-breaks for the package making the fix.

Just to clarify for anyone coming to this issue that this would only be the case for packages supporting PHP <= 7.0. This 3v4l example demonstrates the options.

Obviously this one is up to you as maintainer but if you aren't going to include this, I'll be copying this sniff and adding the fix to our local ruleset anyway ;)

@andrewnicols I would warn you off from copying the sniff as you would be violating copyright (and offending me).

If you want the most obvious solution - making the parameter nullable - and your codebase's minimum PHP version allows for it, I would recommend you include the SlevomatCodingStandard.TypeHints.NullableTypeForNullDefaultValue sniff in your coding standard, which was also mentioned in the RFC at my recommendation. That sniff will auto-fix the issue as a matter of code style.

@andrewnicols I would warn you off from copying the sniff as you would be violating copyright (and offending me).

No offense is intended. My understanding was that this sniff is licensed under the LGPL3 though, which I understood would permit copying and modifying as required. In any case, I do not intend to upset or offend.

If you want the most obvious solution - making the parameter nullable - and your codebase's minimum PHP version allows for it, I would recommend you include the SlevomatCodingStandard.TypeHints.NullableTypeForNullDefaultValue sniff in your coding standard, which was also mentioned in the RFC at my recommendation. That sniff will auto-fix the issue as a matter of code style.

The Slevomat sniff is absoltuely massive and has a number of bloated dependencies that we are keen to avoid. This is not a set and forget situation for us as our community has hundreds of plugins that need to be updated in the same way.

I had planned to write my own Sniff so I guess I'll go back down that road.

No offense is intended. My understanding was that this sniff is licensed under the LGPL3 though, which I understood would permit copying and modifying as required. In any case, I do not intend to upset or offend.

IANAL, but as far as I understand it, forking and updating (while retaining the original commits and copyright) is okay. Copying, adjusting and then passing it off as your own, is not.

The Slevomat sniff is absoltuely massive and has a number of bloated dependencies that we are keen to avoid. This is not a set and forget situation for us as our community has hundreds of plugins that need to be updated in the same way.

Could you elaborate on that ? I mean: the Slevomat sniff collection is large, true, but you would only be using one sniff of it in this case.
As for dependencies, they only have three - two of which overlap with PHPCompatibility:

	"require": {
		"php": "^7.2 || ^8.0",
		"dealerdirect/phpcodesniffer-composer-installer": "^0.6.2 || ^0.7 || ^1.0",
		"phpstan/phpdoc-parser": "^1.23.1",
		"squizlabs/php_codesniffer": "^3.9.0"
	},

So, you're only really talking about the phpstan/phpdoc-parser dependency and that dependency has no underlying dependencies either.