[ExpressionLanguage] Support non-existent names when followed by null coalescing

[adamkiss]

Q	A
Branch?	7.2
Bug fix?	no
New feature?	yes
Issues	Fix #54359
License	MIT

This PR allows for null coalescing nonexistent names (nonexistent ?? 123) in expressions by introducing new type of node NullCoalescedNameNode, which compiles to $nonexistent ?? null, so it subsequently evaluates to null and the null coalescing takes over then.

Edit: feature/bug is questionable, because I half-consider it a bug, since it's one of the examples in the docs, despite my original issue being closed as "expected", and the docs issue marked resolved despite this use case throwing while existing names resolving to null pass.

[carsonbot]

Hey!

I see that this is your first PR. That is great! Welcome!

Symfony has a contribution guide which I suggest you to read.

In short:

• Always add tests
• Keep backward compatibility (see https://symfony.com/bc).
• Bug fixes must be submitted against the lowest maintained branch where they apply (see https://symfony.com/releases)
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Review the GitHub status checks of your pull request and try to solve the reported issues. If some tests are failing, try to see if they are failing because of this change.

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I am going to sit back now and wait for the reviews.

Cheers!

Carsonbot

[OskarStark]

To me this a new feature, please add an entry in the changeling for 7.2 section, as we are in feature freeze for 7.1, thanks

[adamkiss]

To me this a new feature, please add an entry in the changeling for 7.2 section, as we are in feature freeze for 7.1, thanks

Shame about the feature freeze. will do.

[fabpot]

Thank you @adamkiss.