[php-src] Issue #9655: PHP8.2 Disjunctive Normal Form Types with a default value of null

Issue: https://github.com/php/php-src/issues/9655 Author: HypeMC ### Description There seems to be some inconsistent behavior with Disjunctive Normal Form Types when an argument has a default value of null. Usually if the default value is null, the argument is implicitly nullable, eg: ```php <?php function foo(string $param = null) { var_dump($param); } function bar(\Foo\Bar|\Foo\Baz $param = null) { var_dump($param); } foo(null); bar(null); ``` result: ``` NULL NULL ``` https://3v4l.org/iBlne An exception to this rule are PHP 8.1 intersection types: ```php function foo(\Foo\Bar&\Foo\Baz $param = null) { var_dump($param); } foo(null); ``` result: ``` Fatal error: Cannot use null as default value for parameter $param of type Bar\Baz&Bar\Qux in /in/FEKsq on line 3 Process exited with code 255. ``` https://3v4l.org/k0OjD However, the same error is raised on PHP 8.2, even though the following works: ```php function foo((\Foo\Bar&\Foo\Baz)|\Foo\Qux $param = null) { var_dump($param); } foo(null); ``` result: ``` NULL ``` https://3v4l.org/UADDP With the introduction of DNF types, I would expect \Foo\Bar&\Foo\Baz $param = null to implicitly mean (\Foo\Bar&\Foo\Baz)|null $param = null, which works as expected: ```php function foo((\Foo\Bar&\Foo\Baz)|null $param = null) { var_dump($param); } foo(null); ``` result: ``` NULL ``` https://3v4l.org/gjOAp ### PHP Version PHP 8.2rc3 ### Operating System Ubuntu 22.04