…(ro0NL)This PR was squashed before being merged into the 4.1 branch (closes#28838).Discussion----------[DI] Default undefined env to empty string during compile| Q             | A| ------------- | ---| Branch?       | 4.1| Bug fix?      | yes| New feature?  | no| BC breaks?    | no     <!-- seehttps://symfony.com/bc -->| Deprecations? | no| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->| Fixed tickets |#28827| License       | MIT| Doc PR        | symfony/symfony-docs#... <!-- required for new features -->Instead of using `null` for undefined envs, use `""` instead. We already default the type to string, so actually providing a string value makes sense. During runtime it will always be string also.Commits-------38a8ab9 [DI] Default undefined env to empty string during compile

…o0NL)This PR was squashed before being merged into the 4.3-dev branch (closes#28858).Discussion----------[DI] Deprecated using env vars with cannotBeEmpty()| Q             | A| ------------- | ---| Branch?       | master| Bug fix?      | yes-ish| New feature?  | yes| BC breaks?    | no     <!-- seehttps://symfony.com/bc -->| Deprecations? | yes| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->| Fixed tickets |#28827| License       | MIT| Doc PR        | symfony/symfony-docs#... <!-- required for new features -->Continuation of#28838 for 4.2Using environment variables for nodes marked `cannotBeEmpty()` is semantically not possible, we'll never know the value is empty yes/no during compile time. Neither we should assume one or another.Commits-------397c19e [DI] Deprecated using env vars with cannotBeEmpty()