bug #23341 [DoctrineBridge][Security][Validator] do not validate empty values (xabbuh)

This PR was merged into the 2.7 branch.

Discussion
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[DoctrineBridge][Security][Validator] do not validate empty values

| Q             | A
| ------------- | ---
| Branch?       | 2.7
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #23319
| License       | MIT
| Doc PR        |

Nearly all validators operating on scalar values (except for some special constraints) do ignore empty values. If you want to forbid them, you have to use the `NotBlank` constraint instead.

Commits
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fd7ad234bc do not validate empty values

Author: fabpot

Constraints/UrlValidator.php

@@ -48,7 +48,7 @@ public function validate($value, Constraint $constraint)
             throw new UnexpectedTypeException($constraint, __NAMESPACE__.'\Url');
         }
 
-        if (null === $value) {
+        if (null === $value || '' === $value) {
             return;
         }