…alues (dunglas)

This PR was squashed before being merged into the 4.3-dev branch (closes #29641).

Discussion
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[Validator] NotBlank: add a new option to allow null values

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes <!-- don't forget to update src/**/CHANGELOG.md files -->
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no <!-- don't forget to update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets | #27876
| License       | MIT
| Doc PR        | todo

This PR adds a new option to the `@NotBlank` constraint to allow null values. As described in #27876, this is particularly useful when creating web APIs.

Commits
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484d22a [Validator] NotBlank: add a new option to allow null values

…aviereguiluz)

This PR was merged into the master branch.

Discussion
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Document the allowNull option for NotBlank constraint

This documents symfony/symfony#29641

Commits
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ab2c4f1 Document the allowNull option for NotBlank constraint

…reject empty strings (ogizanagi)

This PR was merged into the 4.4 branch.

Discussion
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[Validator] Add a Length::$allowEmptyString option to reject empty strings

| Q             | A
| ------------- | ---
| Branch?       | 4.4 <!-- see below -->
| Bug fix?      | no
| New feature?  | yes <!-- please update src/**/CHANGELOG.md files -->
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | yes <!-- please update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets | N/A   <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        | Todo (change the warning on top of https://symfony.com/doc/current/reference/constraints/Length.html)

which defaults to `true` in 4.4 but will trigger a deprecation if not set explicitly
in order to make the default `false` in 5.0.

While it could be solved now thanks to #29641 by using both `@Length(min=1)` & `@NotBlank(allowNull=true)` constraints,
as expressed in #27876 (comment) and following comments, the `@Length(min=1)` behavior doesn't match our expectations when reading it: it feels logical to invalidate empty strings, but it actually doesn't.
Hence the proposal of making the behavior of rejecting empty strings the default in 5.0.

In my opinion, the flag could even be removed later.

Commits
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e113e7f [Validator] Add a Length::$allowEmptyString option to reject empty strings