[php-src] Issue #8204: Nullsafe Operator doesn't work with uninitialized properties

Issue: https://github.com/php/php-src/issues/8204 Comment Author: iw-rylee I think the biggest confusion here is that another operator interacting with null works: ```php ($this->date_val ?? null)?->format("Y-m-d") ?? "default" ``` This doesn't throw the error, but it's labelled as "Null coalescing operator"[ ¶](https://www.php.net/manual/en/migration70.new-features.php#migration70.new-features.null-coalesce-op). From that, I would think that something labelled "Nullsafe operator" [ ¶](https://www.php.net/releases/8.0/en.php#nullsafe-operator) works with values/properties in the same way. It seems they have *very* similar naming but different underlying logic. I understand that the documentation for "Null coalescing operator" explains that it's essentially a replacement for cases where isset() is used with a ternary operator. There doesn't seem to be the same level of documentation (that I could find easily) that explains *how* the "Nullsafe operator" works. For consistency, it seems sensible (to me at least) that either both throw an exception, or both work. Is there a reason one guards against IS_UNDEF and the other doesn't?