…yntax (mytuny)This PR was merged into the 6.2 branch.Discussion----------[ExpressionLanguage] Add support for null coalescing syntax| Q             | A| ------------- | ---| Branch?       | 6.1| Bug fix?      | no| New feature?  | yes| Deprecations? | no| Tickets       |Fix#45411,#21691| License       | MIT| Doc PR        |symfony/symfony-docs#16743This is another waited feature for the syntax of the expression-language component. The [null-coalescing](https://wiki.php.net/rfc/isset_ternary) operator ``??`` becomes a need for variant programming needs these days.Following my previous PR introducing the null-safe operator (#45795). I'm hereby introducing yet another essential operator to make the syntax even more complete.The null-coalescing operator is a syntactic sugar for a common use of ternary in conjunction with ``isset()`` (in PHP) or equivalent in other languages. This is such a common use-case to the point that almost all majors programming syntax nowadays support a sort of a short-hand for that operation namely coalescing operator. Now it's time for the syntax of Expression-Language to do so!Expressions like:* ``foo.bar ?? 'default'``* ``foo[3] ?? 'default'``* ``foo.bar ?? foo['bar'] ?? 'default'``will default to the expression in the right-hand-side of the ``??`` operator whenever the expression in the left-hand-side of it does not exist or it's ``null``. Note that this coalescing behavior can be chained and the validation logic takes decreasing priority from left to right.Commits-------8e3c505 [ExpressionLanguage] Add support for null coalescing syntax